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The internal organization of cells is largely determined by the architecture and orientation of the microtubule network. Microtubules serve as polar tracks for the selective transport of specific molecular motors toward either their plus or minus ends. How both motors reciprocally move microtubules and organize the network's arrangement and polarity is unknown. Here, we combined experiments on reconstituted systems and theory to study the interaction of microtubules with both plus-and minus-end directed motors bound to a fluid membrane. Depending on motor concentrations, the system could lead either to the constant transport of microtubules or to their alignment, stacking, and immobilization in regular bands that separate motors into domains of opposite polarities. In bands, microtubules shared the same polarity and segregated the two opposing motors accordingly. These regular patterns resulted from the balance of forces produced by the two motors as they walked in opposite directions along microtubules. The system was maintained in a dynamic steady state in which the directional transport of microtubule-bound motors compensates for the random diffusion of lipid-bound motors. The size of motor domains depended on their respective concentrations. The constant flow of motors allowed the system to respond to variations in motor concentrations by moving microtubules to adapt to the new force balance. The polar sorting and linear arrangement of microtubules associated with the segregation of motors of opposite polarity are typical of cellular architectures, which these data may help to better understand. [ABSTRACT FROM AUTHOR]

Light‐driven molecular rotary motors convert the energy of absorbed light into unidirectional rotational motion and are key components in the design of molecular machines. The archetypal class of light‐driven rotary motors is chiral overcrowded alkenes, where the rotational movement is achieved through consecutive cis‐trans photoisomerization reactions and thermal helix inversion steps. While the thermal steps have been rather well understood by now, our understanding of the photoisomerization reactions of overcrowded alkene‐based motors still misses key points that would explain the striking differences in operation efficiency of the known systems. Here, we employ quantum‐chemical calculations and nonadiabatic molecular dynamics simulations to investigate the excited‐state decay and photoisomerization mechanism in a prototypical alkene‐based first‐generation rotary motor. We show that the initially excited bright state undergoes an ultrafast relaxation to multiple excited‐state minima separated by low energy barriers and reveal a slow picosecond‐timescale decay to the ground state, which only occurs from a largely twisted dark excited‐state minimum, far from any conical‐intersection point. Additionally, we attribute the origin of the high yields of forward photoisomerization in our investigated motor to the favorable topography of the ground‐state potential energy surface, which is controlled by the conformation of the central cyclopentene rings. [ABSTRACT FROM AUTHOR]

While biological machines are powered mainly by chemical transformations, chemically driven artificial rotary motor systems are very limited. Here, we report an aniline‐phenol‐based rotary molecular motor that operates via an information ratchet mechanism. The 360° directional rotation about a single covalent bond can be chemically driven by reversible oxazepine formation. Both the oxazepine formation and hydrolysis steps are kinetically gated via dynamic kinetic resolution, arising from the kinetic bias of chiral catalysts for enantiomers. Given the 95 % ee (97.5 : 2.5) and 88 % ee (94 : 6) of the individual gating steps of motor analogues, the overall directionality ratio could be calculated to be 91.7 : 8.3 (97.5 %×94 %≈91.7 %), which means that the motor will make one mistake (backward rotation) approximately every 11 to 12 turns. [ABSTRACT FROM AUTHOR]

Towards complex coupled molecular motions, the remote handedness inversion of a helicene moiety was achieved by a rotary molecular motor. The use of a specifically engineered dynamic helicene stator in a novel overcrowded‐alkene second‐generation molecular motor based on a fluorinated dibenzofluorene fragment allows for an unprecedented control over helicity inversion. This is achieved by the mechanical coupling of the rotation of the rotor to the helicene inversion of the stator half via a remote chirality transmission process. Thus, the unidirectional rotary motion generated upon irradiation is used to invert the dynamic stereochemistry of a helicene, leading to a 6‐step cycle with eight intermediates. In this cycle, both alternation between P and M configurations of the helicene stator and dynamic thermal interconversion (paddling motion) can be achieved. In‐depth computational and spectroscopic studies were performed to support the associated mechanism. The control over coupled motion and dynamic helicity offers prospects for the development of complex responsive systems. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is marked by the gradual and age-related deterioration of nerve cells in the central nervous system. The histopathological features observed in the brain affected by AD are the aberrant buildup of extracellular and intracellular amyloid-β and the formation of neurofibrillary tangles consisting of hyperphosphorylated tau protein. Axonal transport is a fundamental process for cargo movement along axons and relies on molecular motors like kinesins and dyneins. Kinesin's responsibility for transporting crucial cargo within neurons implicates its dysfunction in the impaired axonal transport observed in AD. Impaired axonal transport and dysfunction of molecular motor proteins, along with dysregulated signaling pathways, contribute significantly to synaptic impairment and cognitive decline in AD. Dysregulation in tau, a microtubule-associated protein, emerges as a central player, destabilizing microtubules and disrupting the transport of kinesin-1. Kinesin-1 superfamily members, including kinesin family members 5A, 5B, and 5C, and the kinesin light chain, are intricately linked to AD pathology. However, inconsistencies in the abundance of kinesin family members in AD patients underline the necessity for further exploration into the mechanistic impact of these motor proteins on neurodegeneration and axonal transport disruptions across a spectrum of neurological conditions. This review underscores the significance of kinesin-1's anterograde transport in AD. It emphasizes the need for investigations into the underlying mechanisms of the impact of motor protein across various neurological conditions. Despite current limitations in scientific literature, our study advocates for targeting kinesin and autophagy dysfunctions as promising avenues for novel therapeutic interventions and diagnostics in AD. [ABSTRACT FROM AUTHOR]

Cell biologists, including those seeking molecular mechanistic explanations of cellular phenomena, frequently rely on experimental strategies focused on identifying the cellular context relevant to their investigations. We suggest that such practices can be understood as a guided decomposition strategy, where molecular explanations of phenomena are defined in relation to natural contextual (cell) boundaries. This “top-down” strategy contrasts with “bottom-up” reductionist approaches where well-defined molecular structures and activities are orphaned by their displacement from actual biological functions. We focus on the central role of microscopic imaging in cell biology to uncover possible constraints on the system. We show how identified constraints are used heuristically to limit possible mechanistic explanations to those that are biologically meaningful. Historical examples of this process described here include discovery of the mechanism of oxidative phosphorylation in mitochondria, molecular explanation of the first steps in protein secretion, and identification of molecular motors. We suggest that these instances are examples of a form of downward causation or, more specifically, constraining relations, where higher-level structures and variables delimit and enable lower-level system states. The guided decomposition strategy in our historical cases illustrates the irreducibility of experimentally identified constraints in explaining biological activities of cells. Rather than viewing decomposition and recomposition as separate epistemic activities, we contend that they need to be iteratively integrated to account for the ontological complexity of multi-level systems. [ABSTRACT FROM AUTHOR]

Artificial molecular motors have been presented as models for biological molecular motors. In contrast to the conventional artificial molecular motors that rely on covalent bond rotation, molecular motors with mechanically interlocked molecules (MIMs) have attracted considerable attention owing to their ability to generate significant rotational motion by dynamically shuttling macrocyclic components. The topology of MIM‐type rotational molecular motors is currently limited to catenane structures, which require intricate synthetic procedures that typically produce a low synthetic yield. In this study, we develop a novel class of MIM‐type molecular motors with a rotaxane‐type topology. The switching of the threading/dethreading pathways of the linked rotaxane by protecting/deprotecting the bulky stopper group and changing the solvent polarity enables a net unidirectional rotation of the molecular motor. The threading/dethreading reaction rates were quantitatively evaluated through detailed spectroscopic investigations. Repeated net unidirectional rotation and switching of the direction of rotation were also achieved. Our findings demonstrate that linked rotaxanes can serve as MIM‐type molecular motors with reversible rotational direction controlled by threading/dethreading reactions. These motors hold potential as components of molecular machinery. [ABSTRACT FROM AUTHOR]

Top‐down control of small motion is possible through top‐down controlled molecular motors in replacement of larger actuators like MEMS or NEMS (micro‐ or nano‐electromechanical systems) in the current precision technology. Improving top‐down control of molecular motors to every single step is desirable for this purpose, and also for synchronization of motor actions for amplified effects. Here we report a designed single‐stranded DNA molecular motor powered by alternated ultraviolet and visible light for processive track‐walking, with the two light colours each locking the motor in a full directional step to allow saturated driving but no overstepping. This novel nano‐optomechanical driving mechanism pushes the top‐down control of molecular motors down to every single step, thus providing a key technical capability to advance the molecular motor‐based precision technology and also motor synchronization for amplified effects. [ABSTRACT FROM AUTHOR]

Over the last two decades ratchet mechanisms have transformed the understanding and design of stochastic molecular systems—biological, chemical and physical—in a move away from the mechanical macroscopic analogies that dominated thinking regarding molecular dynamics in the 1990s and early 2000s (e.g. pistons, springs, etc), to the more scale‐relevant concepts that underpin out‐of‐equilibrium research in the molecular sciences today. Ratcheting has established molecular nanotechnology as a research frontier for energy transduction and metabolism, and has enabled the reverse engineering of biomolecular machinery, delivering insights into how molecules 'walk' and track‐based synthesisers operate, how the acceleration of chemical reactions enables energy to be transduced by catalysts (both motor proteins and synthetic catalysts), and how dynamic systems can be driven away from equilibrium through catalysis. The recognition of molecular ratchet mechanisms in biology, and their invention in synthetic systems, is proving significant in areas as diverse as supramolecular chemistry, systems chemistry, dynamic covalent chemistry, DNA nanotechnology, polymer and materials science, molecular biology, heterogeneous catalysis, endergonic synthesis, the origin of life, and many other branches of chemical science. Put simply, ratchet mechanisms give chemistry direction. Kinetic asymmetry, the key feature of ratcheting, is the dynamic counterpart of structural asymmetry (i.e. chirality). Given the ubiquity of ratchet mechanisms in endergonic chemical processes in biology, and their significance for behaviour and function from systems to synthesis, it is surely just as fundamentally important. This Review charts the recognition, invention and development of molecular ratchets, focussing particularly on the role for which they were originally envisaged in chemistry, as design elements for molecular machinery. Different kinetically asymmetric systems are compared, and the consequences of their dynamic behaviour discussed. These archetypal examples demonstrate how chemical systems can be driven inexorably away from equilibrium, rather than relax towards it. [ABSTRACT FROM AUTHOR]

Rotavirus (RV) replicates within viroplasms, membraneless electron-dense globular cytosolic inclusions with liquid–liquid phase properties. In these structures occur the virus transcription, replication, and packaging of the virus genome in newly assembled double-layered particles. The viroplasms are composed of virus proteins (NSP2, NSP5, NSP4, VP1, VP2, VP3, and VP6), single- and double-stranded virus RNAs, and host components such as microtubules, perilipin-1, and chaperonins. The formation, coalescence, maintenance, and perinuclear localization of viroplasms rely on their association with the cytoskeleton. A stabilized microtubule network involving microtubules and kinesin Eg5 and dynein molecular motors is associated with NSP5, NSP2, and VP2, facilitating dynamic processes such as viroplasm coalescence and perinuclear localization. Key post-translation modifications, particularly phosphorylation events of RV proteins NSP5 and NSP2, play pivotal roles in orchestrating these interactions. Actin filaments also contribute, triggering the formation of the viroplasms through the association of soluble cytosolic VP4 with actin and the molecular motor myosin. This review explores the evolving understanding of RV replication, emphasizing the host requirements essential for viroplasm formation and highlighting their dynamic interplay within the host cell. [ABSTRACT FROM AUTHOR]

Alzheimer’s disease (AD) is marked by the gradual and age-related deterioration of nerve cells in the central nervous system. The histopathological features observed in the brain affected by AD are the aberrant buildup of extracellular and intracellular amyloid-β and the formation of neurofibrillary tangles consisting of hyperphosphorylated tau protein. Axonal transport is a fundamental process for cargo movement along axons and relies on molecular motors like kinesins and dyneins. Kinesin’s responsibility for transporting crucial cargo within neurons implicates its dysfunction in the impaired axonal transport observed in AD. Impaired axonal transport and dysfunction of molecular motor proteins, along with dysregulated signaling pathways, contribute significantly to synaptic impairment and cognitive decline in AD. Dysregulation in tau, a microtubule-associated protein, emerges as a central player, destabilizing microtubules and disrupting the transport of kinesin-1. Kinesin-1 superfamily members, including kinesin family members 5A, 5B, and 5C, and the kinesin light chain, are intricately linked to AD pathology. However, inconsistencies in the abundance of kinesin family members in AD patients underline the necessity for further exploration into the mechanistic impact of these motor proteins on neurodegeneration and axonal transport disruptions across a spectrum of neurological conditions. This review underscores the significance of kinesin-1’s anterograde transport in AD. It emphasizes the need for investigations into the underlying mechanisms of the impact of motor protein across various neurological conditions. Despite current limitations in scientific literature, our study advocates for targeting kinesin and autophagy dysfunctions as promising avenues for novel therapeutic interventions and diagnostics in AD.

Photoresponsive supramolecular polymers have a major potential for applications in responsive materials that are externally triggered by light with spatio‐temporal control of their polymerisation state. While changes in macroscopic properties revealed the adaptive nature of these materials, it remains challenging to capture the dynamic depolymerisation process at the molecular level, which requires fast observation techniques combined with in situ irradiation. By implementing in situ UV illumination into a High‐Speed Atomic Force Microscope (HS‐AFM) setup, we have been able to capture the disassembly of a light‐driven molecular motor‐based supramolecular polymer. The real‐time visualisation of the light‐triggered disassembly process not only reveals cooperative depolymerisation, it also shows that this process continues after illumination is halted. Combining the data with cryo‐electron microscopy and spectroscopy approaches, we obtain a molecular‐level description of the motor‐based polymer dynamics reminiscent of actin chain‐end depolymerisation. Our detailed understanding of supramolecular depolymerisation will drive the development of future responsive polymer systems. [ABSTRACT FROM AUTHOR]

Immobilization of stimulus‐responsive systems on solid surfaces is beneficial for controlled signal transmission and adaptive behavior while allowing the characterization of the functional interface with high sensitivity and high spatial resolution. Positioning of the stimuli‐responsive units with nanometer‐scale precision across the adaptive surface remains one of the bottlenecks in the extraction of cooperative function. Nanoscale organization, cooperativity, and amplification remain key challenges in bridging the molecular and the macroscopic worlds. Here we report on the design, synthesis, and scanning tunneling microscopy (STM) characterization of overcrowded alkene photoswitches merged in self‐assembled networks physisorbed at the solid‐liquid interface. A detailed anchoring strategy that ensures appropriate orientation of the switches with respect to the solid surface through the use of bis‐urea groups is presented. We implement a co‐assembly strategy that enables the merging of the photoswitches within physisorbed monolayers of structurally similar 'spacer' molecules. The self‐assembly of the individual components and the co‐assemblies was examined in detail using (sub)molecular resolution STM which confirms the robust immobilization and controlled orientation of the photoswitches within the spacer monolayers. The experimental STM data is supported by detailed molecular mechanics (MM) simulations. Different designs of the switches and the spacers were investigated which allowed us to formulate guidelines that enable the precise organization of the photoswitches in crystalline physisorbed self‐assembled molecular networks. [ABSTRACT FROM AUTHOR]

Dynein, an ancient microtubule-based motor protein, performs diverse cellular functions in nearly all eukaryotic cells, with the exception of land plants. It has evolved into three subfamilies—cytoplasmic dynein-1, cytoplasmic dynein-2, and axonemal dyneins—each differentiated by their cellular functions. These megadalton complexes consist of multiple subunits, with the heavy chain being the largest subunit that generates motion and force along microtubules by converting the chemical energy of ATP hydrolysis into mechanical work. Beyond this catalytic core, the functionality of dynein is significantly enhanced by numerous non-catalytic subunits. These subunits are integral to the complex, contributing to its stability, regulating its enzymatic activities, targeting it to specific cellular locations, and mediating its interactions with other cofactors. The diversity of non-catalytic subunits expands dynein's cellular roles, enabling it to perform critical tasks despite the conservation of its heavy chains. In this review, we discuss recent findings and insights regarding these non-catalytic subunits. [ABSTRACT FROM AUTHOR]

We propose a general mathematical and computational approach to study cellular transport driven by a group of kinesin motors. It is a framework for multi-scale modeling that integrates kinetic models of single kinesin motors, including detachment and reattachment events, to study group behaviors of several motors. By formulating the problem as a semi-Markov process and applying a central limit theorem, asymptotic velocity and diffusivity can be readily calculated, which offers considerable computational advantage over Monte Carlo simulations in tasks such as parameter sensitivity analysis and model selection. We demonstrate the method with some examples. The importance of incorporating the intrinsic microscopic-level dynamics of individual motors is illustrated by showing how changes at the microscopic level propagate to the motor-cargo complex at a mesoscopic level. Particularly, we showcase an example in which changes in the second moment of single-motor characteristics gives rise to different first moment characteristics of the motor group. [ABSTRACT FROM AUTHOR]

Microtubules and molecular motors are essential components of the cellular cytoskeleton, driving fundamental processes in vivo, including chromosome segregation and cargo transport. When reconstituted in vitro, these cytoskeletal proteins serve as energy-consuming building blocks to study the self-organization of active matter. Cytoskeletal active gels display rich emergent dynamics, including extensile flows, locally contractile asters, and bulk contraction. However, it is unclear how the protein–protein interaction kinetics set their contractile or extensile nature. Here, we explore the origin of the transition from extensile bundles to contractile asters in a minimal reconstituted system composed of stabilized microtubules, depletant, adenosine 5′-triphosphate (ATP), and clusters of kinesin-1 motors. We show that the microtubule-binding and unbinding kinetics of highly processive motor clusters set their ability to end-accumulate, which can drive polarity sorting of the microtubules and aster formation. We further demonstrate that the microscopic time scale of end-accumulation sets the emergent time scale of aster formation. Finally, we show that biochemical regulation is insufficient to fully explain the transition as generic aligning interactions through depletion, cross-linking, or excluded volume interactions can drive bundle formation despite end-accumulating motors. The extensile-to-contractile transition is well captured by a simple self-assembly model where nematic and polar aligning interactions compete to form either bundles or asters. Starting from a five-dimensional organization phase space, we identify a single control parameter given by the ratio of the different component concentrations that dictates the material-scale organization. Overall, this work shows that the interplay of biochemical and mechanical tuning at the microscopic level controls the robust self-organization of active cytoskeletal materials. [ABSTRACT FROM AUTHOR]

There has been great endeavor to engineer molecular rotors operated by an electrical current. A frequently met operation principle is the transfer of angular momentum taken from the incident flux. In this paper, we present an alternative driving agent that works also in situations where angular momentum of the incoming flux is conserved. This situation arises typically with molecular rotors that exhibit an easy axis of rotation. For quantitative analysis we investigate here a classical model where molecule and wires are represented by a rigid curved path. We demonstrate that in the presence of chirality, the rotor generically undergoes a directed motion, provided that the incident current exceeds a threshold value. Above this threshold, the corresponding rotation frequency (per incoming particle current) for helical geometries turns out to be 2πm/M1, where m/M1 is the ratio of the mass of an incident charge carrier and the mass of the helix per winding number.

Molecular motor can be defined as the collection of a separate number of molecular features (that is, a supramolecular structure) which has been developed to carry out a function through the mechanical movements of its components, which occurs when it is appropriately stimulated externally. Therefore, molecular motors include a part with a motor, which is a tool with the power of turning energy to mechanical work. Molecular motors and machines operate by means of nuclear rearrangements, which like their macroscopic peers, and are described by the type of energy input provided to make them function, the way in which their operation can be observed, the potential to renew the operation at will, i.e., setting up of a cyclic process, the time scale needed to complete a cycle of operation, and the performed function. Due to progresses made in several branches of chemistry, it has become possible to design and construct basic prototypes of artificial molecular motors and machines so that we can better understand the mechanisms by which molecular motors of the biological world operate. The expansion of the concept of motors to the molecular level has received great importance not only in the whole research areas but also in the advancement of nanoscience and the development of nanotechnology. Today, molecular motors are one of the common areas of research between biotechnology and nanoscience. These devices are nanoscale motors that have the ability to perform mechanical movements in exchange for a suitable external stimulus. This stimulation can be caused by a chemical reaction, environmental changes, or light exposure. To date, a large number of high-efficiency natural molecular motors have been identified that can be imitated to develop a wide range of synthetic molecular motors. Although the net weight of Nano motors is in the range of molecular units, these nanoscale structures are capable of generating force at very small levels of Pico and fete newton, and with their self-assembly ability can produce large forces (such as those produced in human muscle). These motors obtain their energy through chemical or optical excitation and convert it into mechanical work. Also, the amount of productive force and its efficiency were examined. Molecular motors are known for having a vast variety of types. One of the best possible classifications is based on the origin of the motors. Therefore, molecular motors can be divided into natural and artificial. Natural molecular motors are protein-based, and the fuel they need is supplied by ATP. The synthetic type is either based on DNA molecules or based on chemical (inorganic) compounds. DNA-based synthetic molecular motors derive their energy from DNA. In contrast, the energy of chemical molecular motors can be supplied by various methods such as optical excitation and electrochemical reaction. In this paper, the general introduction of molecular motors and their operating mechanism, as well as the types of molecular motors and electronic and non-electronic applications of molecular motors will be discussed.

Abstract Natural molecular machines have inspired the development of artificial molecular machines, which have the potential to revolutionize several areas of technology. Artificial molecular machines commonly employ molecular switches, molecular motors, and molecular shuttles as fundamental building blocks. The observation of artificial molecular machines constructed by these building blocks can be highly challenging due to their small sizes and intricate behaviors. The use of modern instrumentation and advanced observational techniques plays a crucial role in the observation and characterization of molecular machines. Furthermore, a well‐designed molecular structure is also a critical factor in making molecular machines more observable. This review summarizes the common methods from diverse perspectives used to observe molecular machines and emphasizes the significance of comprehending their behaviors in the design of superior artificial molecular machines.

Molecular motors, based on overcrowded alkenes (L) serving as ligands to chelate lanthanide nitrate, afford the first lanthanide‐functionalized water‐soluble ionic compound [L2‐Ln(NO3)2(H2O)2]·NO3 (LnL2). Benefitting from the "pull–push" feature of L together with 3LMCT from L to LnIII, irradiation with visible light not only drives photochemical isomerization but also induces energy transfer from L to LnIII, decreasing their intensity of low‐energy 3LMCT (ligand‐to‐metal triplet energy transfer) absorptions and sensitizing the Ln‐based luminescence. Thus, the typical EuIII‐based luminescence of EuL2 favors tracing its movement by time‐resolved luminescence, and temperature‐dependent luminescence renders it possibly to be used as potential luminescent thermometers. Very excitingly, besides a contraction of the stator by Ln–L interactions on decreasing the steric hindrance on the "fjord region," the efficiency of intramolecular 3LMCT sensitization synergetically regulates the rotary motion of lanthanide‐complexed motors in thermal helix inversion steps. [ABSTRACT FROM AUTHOR]

Simulations can help unravel the complicated ways in which molecular structure determines function. Here, we use molecular simulations to show how slight alterations of a molecular motor's structure can cause the motor's typical dynamical behavior to reverse directions. Inspired by autonomous synthetic catenane motors, we study the molecular dynamics of a minimal motor model, consisting of a shuttling ring that moves along a track containing interspersed binding sites and catalytic sites. The binding sites attract the shuttling ring while the catalytic sites speed up a reaction between molecular species, which can be thought of as fuel and waste. When that fuel and waste are held in nonequilibrium steady-state concentrations, the free energy from the reaction drives directed motion of the shuttling ring along the track. Using this model and nonequilibrium molecular dynamics, we show that the shuttling ring's direction can be reversed by simply adjusting the spacing between binding and catalytic sites on the track. We present a steric mechanism behind the current reversal, supported by kinetic measurements from the simulations. These results demonstrate how molecular simulation can guide future development of artificial molecular motors. [ABSTRACT FROM AUTHOR]

The Dengue Virus (DENV) non-structural protein 3 (NS3) is a multi-functional protein critical in the viral life cycle. The DENV NS3 is comprised of a serine protease domain and a helicase domain. The helicase domain itself acts as a molecular motor, either translocating in a unidirectional manner along single-stranded RNA or unwinding double-stranded RNA, processes fueled by the hydrolysis of nucleoside triphosphates. In this brief review, we summarize our contributions and ongoing efforts to uncover the thermodynamic and mechanistic functional properties of the DENV NS3 as an NTPase and helicase. [ABSTRACT FROM AUTHOR]

The stepping dynamics of cytoskeletal motor proteins determines the dynamics of cargo transport. In its native cellular environment, a molecular motor is subject to forces from several sources including thermal forces and forces ensuing from the interaction with other motors bound to the same cargo. Understanding how the individual motors respond to these forces can allow us to predict how they move their cargo when part of a team. Here, using simulation, we show that details of how the kinesin motor responds to small assisting forces–which, at the moment, are not experimentally constrained-can lead to significant changes in cargo dynamics. Using different models of the force-dependent detachment probability of the kinesin motor leads to different predictions on the run-length of the cargo they carry. These differences emerge from the thermal forces acting on the cargo and transmitted to the motor through the motor tail that tethers the motor head to the microtubule. We show that these differences appear for cargo carried by individual motors or motor teams, and use our findings to propose the use of thermal forces as a probe of kinesin’s response to force in this otherwise inaccessible force regime.

Here, we report computational studies of bidirectional transport in an axon, specifically focusing on predictions when the retrograde motor becomes dysfunctional. We are motivated by reports that mutations in dynein-encoding genes can cause diseases associated with peripheral motor and sensory neurons, such as type 2O Charcot-Marie-Tooth disease. We use two different models to simulate bidirectional transport in an axon: an anterograde-retrograde model, which neglects passive transport by diffusion in the cytosol, and a full slow transport model, which includes passive transport by diffusion in the cytosol. As dynein is a retrograde motor, its dysfunction should not directly influence anterograde transport. However, our modeling results unexpectedly predict that slow axonal transport fails to transport cargos against their concentration gradient without dynein. The reason is the lack of a physical mechanism for the reverse information flow from the axon terminal, which is required so that the cargo concentration at the terminal could influence the cargo concentration distribution in the axon. Mathematically speaking, to achieve a prescribed concentration at the terminal, equations governing cargo transport must allow for the imposition of a boundary condition postulating the cargo concentration at the terminal. Perturbation analysis for the case when the retrograde motor velocity becomes close to zero predicts uniform cargo distributions along the axon. The obtained results explain why slow axonal transport must be bidirectional to allow for the maintenance of concentration gradients along the axon length. Our result is limited to small cargo diffusivity, which is a reasonable assumption for many slow axonal transport cargos (such as cytosolic and cytoskeletal proteins, neurofilaments, actin, and microtubules) which are transported as large multiprotein complexes or polymers. [ABSTRACT FROM AUTHOR]

Molecular motors are essential for the movement and transportation of macromolecules in living organisms. Among them, rotatory motors are particularly efficient. In this study, we investigated the long-term dynamics of the designed left-handed alpha/alpha toroid (PDB: 4YY2), the RBM2 flagellum protein ring from Salmonella (PDB: 6SD5), and the V-type Na + -ATPase rotor in Enterococcus hirae (PDB: 2BL2) using microcanonical and canonical molecular dynamics simulations with the coarse-grained UNRES force field, including a lipid-membrane model, on a millisecond laboratory time scale. Our results demonstrate that rotational motion can occur with zero total angular momentum in the microcanonical regime and that thermal motions can be converted into net rotation in the canonical regime, as previously observed in simulations of smaller cyclic molecules. For 6SD5 and 2BL2, net rotation (with a ratcheting pattern) occurring only about the pivot of the respective system was observed in canonical simulations. The extent and direction of the rotation depended on the initial conditions. This result suggests that rotatory molecular motors can convert thermal oscillations into net rotational motion. The energy from ATP hydrolysis is required probably to set the direction and extent of rotation. Our findings highlight the importance of molecular-motor structures in facilitating movement and transportation within living organisms. [ABSTRACT FROM AUTHOR]

Active nematics represent a relatively new class of materials with liquid crystalline properties that rely on an energy source to maintain their structure and dynamics. In this paper, we focus on the well-known microtubule-kinesin-based active nematic, powered by chemical energy as ATP (Adenosine triphosphate), and report on how ATP depletion impacts active nematic defect dynamics and texture. Using fluorescence microscope video imaging, we measure the time averaged mean defect separations and root mean square velocities of the active flows as a function of time. We also characterise textural changes and the growth of void space in the network after ATP depletion using an image binarization technique. [ABSTRACT FROM AUTHOR]

Chemical Artificial Intelligence (CAI) is a brand-new research line that exploits molecular, supramolecular, and systems chemistry in wetware (i.e., in fluid solutions) to imitate some performances of human intelligence and promote unconventional robotics based on molecular assemblies, which act in the microscopic world, otherwise tough to be accessed by humans. It is undoubtedly worth spreading the news that AI researchers can rely on the help of chemists and biotechnologists to reach the ambitious goals of building intelligent systems from scratch. This article reports the first attempt at building a Chemical Artificial Intelligence knowledge map and describes the basic intelligent functions that can be implemented through molecular and supramolecular chemistry. Chemical Artificial Intelligence provides new tools and concepts to mimic human intelligence because it shares, with biological intelligence, the same principles and materials. It enables peculiar dynamics, possibly not accessible in software and hardware domains. Moreover, the development of Chemical Artificial Intelligence will contribute to a deeper understanding of the strict link between intelligence and life, which are two of the most remarkable emergent properties shown by the Complex Systems we call biological organisms.

Neurotransmitters are released at synapses by synaptic vesicles (SVs), which originate from SV precursors (SVPs) that have traveled along the axon. Because each synapse maintains a pool of SVs, only a small fraction of which are released, it has been thought that axonal transport of SVPs does not affect synaptic function. Here, studying the corticostriatal network both in microfluidic devices and in mice, we find that phosphorylation of the Huntingtin protein (HTT) increases axonal transport of SVPs and synaptic glutamate release by recruiting the kinesin motor KIF1A. In mice, constitutive HTT phosphorylation causes SV over-accumulation at synapses, increases the probability of SV release, and impairs motor skill learning on the rotating rod. Silencing KIF1A in these mice restored SV transport and motor skill learning to wild-type levels. Axonal SVP transport within the corticostriatal network thus influences synaptic plasticity and motor skill learning.

F1-ATPase is a universal multisubunit enzyme and the smallest-known motor that, fueled by the process of ATP hydrolysis, rotates in 120o steps. A central question is how the elementary chemical steps occurring in the three catalytic sites are coupled to the mechanical rotation. Here, we performed cold chase promotion experiments and measured the rates and extents of hydrolysis of preloaded bound ATP and promoter ATP bound in the catalytic sites. We found that rotation was caused by the electrostatic free energy change associated with the ATP cleavage reaction followed by Pi release. The combination of these two processes occurs sequentially in two different catalytic sites on the enzyme, thereby driving the two rotational sub-steps of the 120o rotation. The mechanistic implications of this finding are discussed based on the overall energy balance of the system. General principles of free energy transduction are formulated, and their important physical and biochemical consequences are analyzed. In particular, how exactly ATP performs useful external work in biomolecular systems is discussed. A molecular mechanism of steady-state, trisite ATP hydrolysis by F1-ATPase, consistent with physical laws and principles and the consolidated body of available biochemical information, is developed. Taken together with previous results, this mechanism essentially completes the coupling scheme. Discrete snapshots seen in high-resolution X-ray structures are assigned to specific intermediate stages in the 120o hydrolysis cycle, and reasons for the necessity of these conformations are readily understood. The major roles played by the “minor” subunits of ATP synthase in enabling physiological energy coupling and catalysis, first predicted by Nath's torsional mechanism of energy transduction and ATP synthesis 25 years ago, are now revealed with great clarity. The working of nine-stepped (bMF1, hMF1), six-stepped (TF1, EF1), and three-stepped (PdF1) F1 motors and of the α3β3γ subcomplex of F1 is explained by the same unified mechanism without invoking additional assumptions or postulating different mechanochemical coupling schemes. Some novel predictions of the unified theory on the mode of action of F1 inhibitors, such as sodium azide, of great pharmaceutical importance, and on more exotic artificial or hybrid/chimera F1 motors have been made and analyzed mathematically. The detailed ATP hydrolysis cycle for the enzyme as a whole is shown to provide a biochemical basis for a theory of “unisite” and steady-state multisite catalysis by F1-ATPase that had remained elusive for a very long time. The theory is supported by a probability-based calculation of enzyme species distributions and analysis of catalytic site occupancies by Mg-nucleotides and the activity of F1-ATPase. A new concept of energy coupling in ATP synthesis/hydrolysis based on fundamental ligand substitution chemistry has been advanced, which offers a deeper understanding, elucidates enzyme activation and catalysis in a better way, and provides a unified molecular explanation of elementary chemical events occurring at enzyme catalytic sites. As such, these developments take us beyond binding change mechanisms of ATP synthesis/hydrolysis proposed for oxidative phosphorylation and photophosphorylation in bioenergetics.

In single-molecule experiments, the dynamics of molecular motors are often observed indirectly by measuring the trajectory of an attached bead in a motor–bead assay. In this work, we propose a method to extract the step size and stalling force for a molecular motor without relying on external control parameters. We discuss this method for a generic hybrid model that describes bead and motor via continuous and discrete degrees of freedom, respectively. Our deductions are solely based on the observation of waiting times and transition statistics of the observable bead trajectory. Thus, the method is non-invasive, operationally accessible in experiments and can, in principle, be applied to any model describing the dynamics of molecular motors. We briefly discuss the relation of our results to recent advances in stochastic thermodynamics on inference from observable transitions. Our results are confirmed by extensive numerical simulations for parameters values of an experimentally realized F1-ATPase assay. [ABSTRACT FROM AUTHOR]

Diabetic peripheral neuropathy (DPN) is a chronic and prevalent metabolic disease that gravely endangers human health and seriously affects the quality of life of hyperglycemic patients. More seriously, it can lead to amputation and neuropathic pain, imposing a severe financial burden on patients and the healthcare system. Even with strict glycemic control or pancreas transplantation, peripheral nerve damage is difficult to reverse. Most current treatment options for DPN can only treat the symptoms but not the underlying mechanism. Patients with long-term diabetes mellitus (DM) develop axonal transport dysfunction, which could be an important factor in causing or exacerbating DPN. This review explores the underlying mechanisms that may be related to axonal transport impairment and cytoskeletal changes caused by DM, and the relevance of the latter with the occurrence and progression of DPN, including nerve fiber loss, diminished nerve conduction velocity, and impaired nerve regeneration, and also predicts possible therapeutic strategies. Understanding the mechanisms of diabetic neuronal injury is essential to prevent the deterioration of DPN and to develop new therapeutic strategies. Timely and effective improvement of axonal transport impairment is particularly critical for the treatment of peripheral neuropathies. [ABSTRACT FROM AUTHOR]

The unidirectional rotation of chemically crosslinked light‐driven molecular motors is shown to progressively shift the swelling equilibrium of hydrogels. The concentration of molecular motors and the initial strand density of the polymer network are key parameters to modulate the macroscopic contraction of the material, and both parameters can be tuned using polymer chains of different molecular weights. These findings led to the design of optimized hydrogels revealing a half‐time contraction of approximately 5 min. Furthermore, under inhomogeneous stimulation, the local contraction event was exploited to design useful bending actuators with an energy output 400 times higher than for previously reported self‐assembled systems involving rotary motors. In the present configuration, we measure that a single molecular motor can lift up loads of 200 times its own molecular weight. [ABSTRACT FROM AUTHOR]

Network-based biocomputation (NBC) relies on accurate guiding of biological agents through nanofabricated channels produced by lithographic patterning techniques. Here, we report on the large-scale, wafer-level fabrication of optimized microfluidic channel networks (NBC networks) using electron-beam lithography as the central method. To confirm the functionality of these NBC networks, we solve an instance of a classical non-deterministic-polynomial-time complete ("NP-complete") problem, the subset-sum problem. The propagation of cytoskeletal filaments, e.g., molecular motor-propelled microtubules or actin filaments, relies on a combination of physical and chemical guiding along the channels of an NBC network. Therefore, the nanofabricated channels have to fulfill specific requirements with respect to the biochemical treatment as well as the geometrical confienement, with walls surrounding the floors where functional molecular motors attach. We show how the material stack used for the NBC network can be optimized so that the motor-proteins attach themselves in functional form only to the floor of the channels. Further optimizations in the nanolithographic fabrication processes greatly improve the smoothness of the channel walls and floors, while optimizations in motor-protein expression and purification improve the activity of the motor proteins, and therefore, the motility of the filaments. Together, these optimizations provide us with the opportunity to increase the reliability of our NBC devices. In the future, we expect that these nanolithographic fabrication technologies will enable production of large-scale NBC networks intended to solve substantially larger combinatorial problems that are currently outside the capabilities of conventional software-based solvers. [ABSTRACT FROM AUTHOR]

The 3‐satisfiability Problem (3‐SAT) is a demanding combinatorial problem that is of central importance among the nondeterministic polynomial (NP) complete problems, with applications in circuit design, artificial intelligence, and logistics. Even with optimized algorithms, the solution space that needs to be explored grows exponentially with the increasing size of 3‐SAT instances. Thus, large 3‐SAT instances require excessive amounts of energy to solve with serial electronic computers. Network‐based biocomputation (NBC) is a parallel computation approach with drastically reduced energy consumption. NBC uses biomolecular motors to propel cytoskeletal filaments through nanofabricated networks that encode mathematical problems. By stochastically exploring possible paths through the networks, the cytoskeletal filaments find possible solutions. However, to date, no NBC algorithm for 3‐SAT has been available. Herein, an algorithm that converts 3‐SAT into an NBC‐compatible network format is reported and four small 3‐SAT instances (with up to three variables and five clauses) using the actin–myosin biomolecular motor system are experimentally solved. Because practical polynomial conversions to 3‐SAT exist for many important NP complete problems, the result opens the door to enable NBC to solve small instances of a wide range of problems. [ABSTRACT FROM AUTHOR]

Throughout the cell, motor proteins work together to drive numerous molecular processes and functions. For example, ensembles of myosin motors collectively transport vesicles and organelles, maintain membrane homeostasis, and drive muscle contraction. Studying these motors in groups has become increasingly important with work demonstrating the emergence of ensemble behavior distinct from individual motor behavior. One powerful technique that has been used in the last decade is DNA nanotechnology, which provides precise control over the spacing and organization of patterned motor proteins. Until recently, however, most studies combining DNA nanostructures and molecular motors have been confined to discrete DNA structures with limited attachment points for motor proteins. In this chapter, we describe a new approach for making synthetic motor filaments using DNA nanotubes. To begin, we present methods for preparing myosin VI-labeled nanotubes and testing these nanotubes using a general in vitro motility setup. We then describe how to modify this system to pattern motor proteins and effectors on the nanotubes. Overall, these nanotubes can easily be used to study large ensembles of molecular motors, such as muscle myosin or ciliary dynein, both proteins that work in large motor ensembles to drive key cellular functions., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Viral DNA packaging is a required step in the assembly of many dsDNA viruses. A molecular motor fueled by ATP hydrolysis packages the viral genome to near crystalline density inside a pre-formed prohead shell in ~5 min at room temperature in vitro. We describe procedures for measuring the packaging of single DNA molecules into single viral proheads with optical tweezers. Additionally, we describe techniques for conducting rapid solution exchange measurements that can be used to probe nucleotide-dependent motor-DNA interactions, stall and restart the motor to probe DNA conformational relaxation, and to probe the dynamics of release of the DNA, akin to ejection, in conditions where the motor fully releases its grip. Three viral packaging systems are described in detail: bacteriophages phi29 (φ29), lambda (λ), and T4. Two different approaches are described: 1. With φ29 and T4, prohead-motor complexes can be pre-assembled in bulk and packaging can be initiated in the optical tweezers by "feeding" a single DNA molecule to one of the complexes; 2. with φ29 and λ, packaging can be initiated in bulk then stalled, and a single prohead-motor-DNA complex can then be captured with optical tweezers and restarted. In both cases, the prohead is ultimately attached to one trapped microsphere and the end of the DNA being packaged is attached to a second trapped microsphere such that packaging of the DNA pulls the two microspheres together and the rate of packaging and force generated by the motor is directly measured in real time. These protocols allow for the effect of many experimental parameters on packaging dynamics to be studied such as temperature, ATP concentration, ionic conditions, structural changes to the DNA substrate, and mutations in the motor proteins. Procedures for capturing microspheres with the optical traps and different measurement modes are also described., (© 2025. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

The eukaryotic cytoskeleton is formed in part by microtubules, which are relatively rigid filaments with inherent structural polarity. One consequence of this polarity is that the two ends of a microtubule have different properties with important consequences for their cellular roles. These differences are often challenging to probe within the crowded environment of the cell. Fluorescence microscopy-based in vitro assays with purified proteins and stabilized microtubules have been used to characterize polarity-dependent and end-specific behaviors. These assays require ways to visualize the polarity of the microtubules, which has previously been achieved either by the addition of fluorescently tagged motor proteins with known directionality or by fluorescently polarity marking the microtubules themselves. However, classical polarity-marking protocols require a particular chemically modified tubulin and generate microtubules with chemically different plus and minus segments. These chemical differences in the segments may affect the behavior of interacting proteins of interest in an undesirable manner. We present here a new protocol that uses a previously characterized, reversibly binding microtubule plus-end capping protein, a designed ankyrin repeat protein (DARPin), to efficiently produce polarity-marked microtubules with different fluorescently labeled, but otherwise biochemically identical, plus- and minus-end segments. Key features • Produces polarity-marked microtubules with biochemically identical segments • Allows analysis of end-specific and polarity-dependent activities of purified microtubule-associated proteins • Requires purified microtubule plus-end capping DARPin (D1) 2 • Concentrations optimized for porcine brain tubulin., Competing Interests: Competing interestsThe authors declare no competing interests., (©Copyright : © 2024 The Authors; This is an open access article under the CC BY license.)

Deciphering inter- and intracellular signaling pathways is pivotal for understanding the intricate communication networks that orchestrate life's dynamics. Communication models involving bottom-up construction of protocells are emerging but often lack specialized compartments sufficiently robust and hierarchically organized to perform spatiotemporally defined signaling. Here, the modular construction of communicating polymer-based protocells designed to mimic the transduction of information in retinal photoreceptors is presented. Microfluidics is used to generate polymeric protocells subcompartmentalized by specialized artificial organelles. In one protocell population, light triggers artificial organelles with membrane-embedded photoresponsive rotary molecular motors to set off a sequence of reactions starting with the release of encapsulated signaling molecules into the lumen. Intercellular communication is mediated by signal transfer across membranes to protocells containing catalytic artificial organelles as subcompartments, whose signal conversion can be modulated by environmental calcium. Signal propagation also requires selective permeability of the diverse compartments. By segregating artificial organelles in distinct protocells, a sequential chain of reactions mediating intercellular communication is created that is further modulated by adding extracellular messengers. This connective behavior offers the potential for a deeper understanding of signaling pathways and faster integration of proto- and living cells, with the unique advantage of controlling each step by bio-relevant signals., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Salmonellae are bacteria that cause moderate to severe infections in humans, depending on the strain and the immune status of the infected host. These pathogens have the particularity of residing in the cells of the infected host. They are usually found in a vacuolar compartment that the bacteria shape with the help of effector proteins. Following invasion of a eukaryotic cell, the bacterial vacuole undergoes maturation characterized by changes in localization, composition and morphology. In particular, membrane tubules stretching over the microtubule cytoskeleton are formed from the bacterial vacuole. Although these tubules do not occur in all infected cells, they are functionally important and promote intracellular replication. This review focuses on the role and significance of membrane compartment remodeling observed in infected cells and the bacterial and host cell pathways involved.

The 3‐satisfiability Problem (3‐SAT) is a demanding combinatorial problem that is of central importance among the nondeterministic polynomial (NP) complete problems, with applications in circuit design, artificial intelligence, and logistics. Even with optimized algorithms, the solution space that needs to be explored grows exponentially with the increasing size of 3‐SAT instances. Thus, large 3‐SAT instances require excessive amounts of energy to solve with serial electronic computers. Network‐based biocomputation (NBC) is a parallel computation approach with drastically reduced energy consumption. NBC uses biomolecular motors to propel cytoskeletal filaments through nanofabricated networks that encode mathematical problems. By stochastically exploring possible paths through the networks, the cytoskeletal filaments find possible solutions. However, to date, no NBC algorithm for 3‐SAT has been available. Herein, an algorithm that converts 3‐SAT into an NBC‐compatible network format is reported and four small 3‐SAT instances (with up to three variables and five clauses) using the actin–myosin biomolecular motor system are experimentally solved. Because practical polynomial conversions to 3‐SAT exist for many important NP complete problems, the result opens the door to enable NBC to solve small instances of a wide range of problems.

Myosins are essential components of organelle trafficking in all the eukaryotic cells. Myosin driven movement plays a vital role in the development of pollen tubes, root hairs and root tips of flowering plants. The present research characterized the myosin genes in Arabidopsis thaliana and Helianthus annuus by using different computational tools. We discovered a total of 50 myosin genes and their splice variants in both pant species. Phylogenetic analysis indicated that myosin genes were divided into four subclasses. Chromosomal location revealed that myosin genes were located on all five chromosomes in A. thaliana, whereas they were present on nine chromosomes in H. annuus. Conserved motifs showed that conserved regions were closely similar within subgroups. Gene structure analysis showed that Atmyosin2.2 and Atmyosin2.3 had the highest number of introns/exons. Gene ontology analysis indicated that myosin genes were involved in vesicle transport along actin filament and cytoskeleton trafficking. Expression analysis showed that expression of myosin genes was higher during the flowering stage as compared to the seedling and budding stages. Tissue specific expression indicated that HanMYOSIN11.2, HanMYOSIN16.2 were highly expressed in stamen, whereas HanMYOSIN 2.2, HanMYOSIN 12.1 and HanMYOSIN 17.1 showed higher expression in nectary. This study enhance our understanding the function of myosins in plant development, and forms the basis for future research about the comparative genomics of plant myosin in other crop plants.

V-ATPases are rotary motor proteins that convert the chemical energy of ATP into the electrochemical potential of ions across cell membranes. V-ATPases consist of two rotary motors, Vo and V1, and Enterococcus hirae V-ATPase (EhVoV1) actively transports Na+ in Vo (EhVo) by using torque generated by ATP hydrolysis in V1 (EhV1). Here, we observed ATP-driven stepping rotation of detergent-solubilized EhVoV1 wildtype, aE634A, and BR350K mutants under various Na+ and ATP concentrations ([Na+] and [ATP], respectively) by using a 40-nm gold nanoparticle as a low-load probe. When [Na+] was low and [ATP] was high, under the condition that only Na+ binding to EhVo is rate limiting, wild-type and aE634A exhibited 10 pausing positions reflecting 10-fold symmetry of the EhVo rotor and almost no backward steps. Duration time before the forward steps was inversely proportional to [Na+], confirming that Na+ binding triggers the steps. When both [ATP] and [Na+] were low, under the condition that both Na+ and ATP bindings are rate limiting, aE634A exhibited 13 pausing positions reflecting 10- and 3-fold symmetries of EhVo and EhV1, respectively. The distribution of duration time before the forward step was fitted well by the sum of two exponential decay functions with distinct time constants. Furthermore, occasional backward steps smaller than 36° were observed. Small backward steps were also observed during three long ATP cleavage pauses of BR350K. These results indicate that EhVo and EhV1 do not share pausing positions, Na+ and ATP bindings occur at different angles, and the coupling between EhVo and EhV1 has a rigid component. [ABSTRACT FROM AUTHOR]

Circular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light‐driven molecular motors as photo‐controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non‐invasively by light, opening possibilities for pixilated displays with externally addressable polarization. [ABSTRACT FROM AUTHOR]

Molecular machines are at the frontier of biology and chemistry. The ability to control molecular motion and emulating the movement of biological systems are major steps towards the development of responsive and adaptive materials. Amazing progress has been seen for the design of molecular machines including light‐induced unidirectional rotation of overcrowded alkenes. However, the feasibility of inducing unidirectional rotation about a single bond as a result of chemical conversion has been a challenging task. In this Review, an overview of approaches towards the design, synthesis, and dynamic properties of different classes of atropisomers which can undergo controlled switching or rotation under the influence of a chemical stimulus is presented. They are categorized as molecular switches, rotors, motors, and autonomous motors according to their type of response. Furthermore, we provide a future perspective and challenges focusing on building sophisticated molecular machines. [ABSTRACT FROM AUTHOR]