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Regulation of the crossbridge cycle that drives muscle contraction involves a reconfiguration of the troponin--tropomyosin complex on actin filaments. By comparing atomic models of troponin--tropomyosin fitted to cryo-EM structures of inhibited and Ca2+-activated thin filaments, we find that tropomyosin pivots rather than rolls or slides across actin as generally thought. We propose that pivoting can account for the Ca2+ activation that initiates muscle contraction and then relaxation influenced by troponin-I (TnI). Tropomyosin is well-known to occupy either of three meta-stable configurations on actin, regulating access of myosin motorheads to their actin-binding sites and thus the crossbridge cycle. At low Ca2+ concentrations, tropomyosin is trapped by TnI in an inhibitory B-state that sterically blocks myosin binding to actin, leading to muscle relaxation. Ca2+ binding to TnC draws TnI away from tropomyosin, while tropomyosin moves to a C-state location over actin. This partially relieves the steric inhibition and allows weak binding of myosin heads to actin, which then transition to strong actin-bound configurations, fully activating the thin filament. Nevertheless, the reconfiguration that accompanies the initial Ca2+-sensitive B-state/C-state shift in troponin--tropomyosin on actin remains uncertain and at best is described by moderate-resolution cryo- EM reconstructions. Our recent computational studies indicate that intermolecular residue-to-residue salt-bridge linkage between actin and tropomyosin is indistinguishable in B- and C-state thin filament configurations. We show here that tropomyosin can pivot about relatively fixed points on actin to accompany B-state/C-state structural transitions. We argue that at low Ca2+ concentrations C-terminal TnI domains attract tropomyosin, causing it to bend and then pivot toward the TnI, thus blocking myosin binding and contraction. [ABSTRACT FROM AUTHOR]

Filamentous actin (F-actin) is the major protein of muscle thin filaments, and actin microfilaments are the main component of the eukaryotic cytoskeleton. Mutations in different actin isoforms lead to early-onset [...]

The flooding brought about by compound coastal flooding events can be devastating. Before, during, and immediately following these events, flood inundation maps (FIMs) can provide essential information to emergency management. However, there are a number of frameworks capable of estimating FIMs during flood events. In this article, we evaluate FIMs derived from three such frameworks in the context of Hurricane Harvey. Our analysis reveals that each of the three FIM frameworks provides different FIMs that differ in their level of accuracy. Each of the three FIMs also produces different exposure and consequence estimates because of their spatial differences. This investigation highlights the need for a centralized means of vetting and adjudicating multiple FIMs during compound flood events empowered by the ability to distribute FIMs as geographic information system (GIS) services and coalesce FIMs into a common operating picture. Furthermore, we provide evidence that the ability to produce multi-model estimates of FIMs to create probabilistic FIMs may provide a better product than the use of a lone FIM. [ABSTRACT FROM AUTHOR]

Striated muscle contraction is regulated in a calcium-dependent manner through dynamic motions of the tropomyosin/troponin polymer, a multicomponent complex wrapped around actin-containing thin filaments. Tropomyosin/troponin sterically blocks myosin-binding at low-calcium concentrations but moves to expose myosin-binding sites at high-calcium concentrations leading to force development. Understanding the key intermolecular interactions that define these dynamic motions will promote our understanding of mutation-induced contractile dysfunction that eventually leads to hypertrophic cardiomyopathy, dilated cardiomyopathy, and skeletal myopathies. Advancements in cryoelectron microscopy (cryoEM) have resulted in a partial elucidation of structures of the thin filament, revealing many atomic-level interactions between the component proteins and critical calcium-dependent conformational alterations. However, building models at the resolutions achieved can be challenging since landmarks in the maps are often missing or ambiguous. Therefore, current computational analyses including de novo structure prediction, protein-protein docking, molecular dynamics flexible fitting, and molecular dynamics simulations are needed to ensure good quality models. We review here our efforts to model the troponin T domain spanning the head-to-tail overlap domain of tropomyosin, improving previous models. Next, we refined the published cryoEM modeled structures, which had mistakenly compressed alpha helices, with a model that has expected helical parameters while matching densities in the cryoEM volume. Lastly, we used this model to reinterpret the interactions between tropomyosin and troponin I showing key features that hold the tropomyosin cable in its low-calcium, sterically blocking position. These revised thin filament models show improved intermolecular interactions in the key low- and high-calcium regulatory states, providing novel insights into function. [ABSTRACT FROM AUTHOR]

Simple Summary: As a key element of the smooth muscle cell contractile apparatus, the actin cytoskeleton participates in the development of force by acting as a molecular track for the myosin cross bridge motor. At the same time, the actin cytoskeleton must transmit the force developed during contraction to the extracellular matrix and, thus, to neighboring cells. This propagation of force to the cell periphery and beyond is initiated in part on specifically localized cellular cortical actin filaments also involved in mechano-chemical transduction. During the contractile process itself and in response to extracellular structural and chemical alterations, the smooth muscle actin cytoskeletal remodels. This indicates that the cytoskeleton is a dynamic cellular organelle that adapts to the changes in cell shape and chemical cues. Current evidence connecting contractile function and mechano-transduction mechanisms to the plasticity of the vascular smooth muscle actin cytoskeleton is reviewed; we then describe new evidence for cytoskeletal remodeling in vascular smooth muscle cells. Here, using immunoelectron microscopy, we visualize the actin binding proteins filamin A, zyxin and talin in these cells and show that they participate in the cortical cell cytoskeletal alteration, thus supporting the premise that smooth muscle cell remodeling occurs during contraction. Considerable controversy has surrounded the functional anatomy of the cytoskeleton of the contractile vascular smooth muscle cell. Recent studies have suggested a dynamic nature of the cortical cytoskeleton of these cells, but direct proof has been lacking. Here, we review past studies in this area suggesting a plasticity of smooth muscle cells. We also present images testing these suggestions by using the technique of immunoelectron microscopy of metal replicas to directly visualize the cortical actin cytoskeleton of the contractile smooth muscle cell along with interactions by representative cytoskeletal binding proteins. We find the cortical cytoskeletal matrix to be a branched, interconnected network of linear actin bundles. Here, the focal adhesion proteins talin and zyxin were localized with nanometer accuracy. Talin is reported in past studies to span the integrin–cytoplasm distance in fibroblasts and zyxin is known to be an adaptor protein between alpha-actinin and VASP. In response to activation of signal transduction with the alpha-agonist phenylephrine, we found that no movement of talin was detectable but that the zyxin-zyxin spacing was statistically significantly decreased in the smooth muscle cells examined. Contractile smooth muscle is often assumed to have a fixed cytoskeletal structure. Thus, the results included here are important in that they directly support the concept at the electron microscopic level that the focal adhesion of the contractile smooth muscle cell has a dynamic nature and that the protein–protein interfaces showing plasticity are protein-specific. [ABSTRACT FROM AUTHOR]

The flooding brought about by compound coastal flooding can be devastating. Before, during, and immediately following these events, flood inundation maps, or Events Maps, can provide essential information to emergency management. However, there are a number of frameworks capable of estimating Event Maps during flood events. In this article, we evaluate three such Event Map frameworks in the context of Hurricane Harvey. Our analysis reveals that each of the three frameworks provide different inundation maps that differ in their level of accuracy. Each of the three Event Maps also produce different exposure and consequence estimates because of their physical differences. This investigation highlights the need for a centralized means of vetting and adjudicating multiple Event Maps during compound flood events empowered by the ability to distribute Event Maps as geographic information system (GIS) services and coalesce Event Maps into a common operating picture. Furthermore, we provide evidence that the ability to produce multi-model estimates of Events Maps to create probabilistic Event Maps may provide a better product than the use of a lone Event Map. [ABSTRACT FROM AUTHOR]

The United States Army Corps of Engineers’ Hydrologic Engineering Center developed the HEC-FIA (Flood Impact Analysis) software to assist in the estimation of consequences with uncertainty. By estimating the consequences, the benefits of existing and future flood risk management measures can be evaluated and compared. HEC-FIA utilizes geospatial datasets to help users build structure inventories and assign values and population per structure. Using this information and geospatially derived flood depth grids (provided by most hydraulic models), HEC-FIA estimates direct economic, indirect economic, agricultural, and life loss consequences for flood hazards. HEC-FIA can compute results for a single event in either deterministic mode or in uncertainty mode which utilizes a Monte Carlo approach. The user can define the uncertainties about any structure in the floodplain in many ways, and each has various impacts on the different consequence calculations. For example, foundation heights, structure values, and depth-damage relationships impact economic consequences, while foundation heights, warning issuance times, and fatality rates impact the life loss calculations. All of these parameters can be defined with uncertainty. HEC-FIA can also be linked into HEC-WAT (Watershed Analysis Tool) with the FRA (Flood Risk Analysis) compute option to randomize the hydraulic events being evaluated in HEC-FIA so that hydrologic, hydraulic, geotechnical, and economic uncertainties can all be represented and evaluated by alternative within the floodplain. This paper will describe how HEC-FIA can be utilized to help evaluate the indirect economic consequences for various alternatives within a floodplain. The computational methods for indirect economic losses utilize a Computable General Equilibrium model to describe the secondary and tertiary impacts of loss of service, loss of laborers, and reductions in demand for intermediary goods.

Although flooding can lead to many types of severe consequences, the primary objective of the US Army Corps of Engineers (USACE) dam and levee safety programs are to manage risk to the public who rely on those structures to keep them reasonably safe from flooding. Thus, reducing the risk associated with loss of life is paramount. USACE employs a scalable approach to estimating loss of life, where the goal is to invest an appropriate amount of resources to answer the question at hand. Given the large number of dams and levees within the USACE portfolio (over 700 dams and 15,000 miles of levees), a “one size fits all” approach does not work. Screening level risk assessments are carried out to initially characterize risk. That initial risk characterization informs prioritization of additional efforts such as interim risk management activities and more detailed risk assessments. More detailed risk assessments inform investment in long-term risk reduction measures, which include analysis and selection of major modification activities and implementation of non-structural measures including emergency management and evacuation planning. This paper describes the USACE scalable approach for estimating loss of life from flood events.

The United States Army Corps of Engineers (USACE) guidance documents require economists and planners to meet a very high standard when evaluating consequences resulting from flood events. The guidance documents require analysts to evaluate how government action changes the consequences over time, in addition to evaluating how government inaction changes consequences over time as well. Corps guidance (Engineering Regulation 1105-2-100, Section 2-3.c.4 and Engineering Regulation 1105-2-100, Section 2-3.b respectively) require the evaluation of direct and indirect economic impacts, life risk impacts, and agricultural impacts for both current conditions and future most likely conditions across a range of alternatives. Evaluating the potential for impacts from flooding across time, and how time impacts their existence or vulnerability, is considered a “lifecycle approach”. Little to no guidance is available on the process of calculating this “lifecycle approach” regarding changes in the value and number of assets within the floodplain over time. Performing a lifecycle analysis of a project over durations from 30 to 100 years, depending on the project purpose, requires evaluation of the changes in human behavior caused by changes in the floodplain such as reconstruction of structures, maintenance of structures, construction of new structures, population growth, and what type of structures are being built within the study area. This type of evaluation is not fully supported by most of the software programs utilized for flood risk management in the planning context. This paper is intended to describe pros and cons of economic lifecycle evaluation techniques to address the needs stated by policy, and tools that are being developed to support this analysis.

Objective: We searched for the application of usability in the literature with a focus on adoption, measurements employed, and demonstrated value. Five human factors domains served as a platform for our reflection, which included the last 20 years. Background: As usability studies continue to accumulate, there has been only a little past reflection on usability and contributions across a variety of applications. Our research provides a background for general usability, and we target specific usability research subareas within transportation, aging populations, autistic populations, telehealth, and cybersecurity. Method: "Usability" research was explored across five different domains within human factors. The goal was not to perform an exhaustive review but, rather, sample usability practices within several specific subareas. We focused on answering three questions: How was usability adopted? How was it measured? How was it framed in terms of value? Conclusion: We found that usability is very domain specific. Usability benchmarking studies and empirical standards are rare. The value associated with improving usability ranged widely—from monetary benefits to saving lives. Thus, researchers are motivated to further improve usability practices. A number of data collection and interpretation challenges still call for solutions. Application: Findings offer insight into the development of usability, as applied across a variety of subdomains. Our reflection ought to inform future theory development efforts. We are concerned about the lack of established benchmarks, which can help ground data interpretation. Future research should address this gap in the literature. We note that our findings can be used to develop better training materials for future usability researchers. [ABSTRACT FROM AUTHOR]

The data on warning diffusion rates over time are generally sparse and are extremely limited for hurricanes. This is a potential problem for transportation analysts who are trying to compute evacuation time estimates for coastal jurisdictions. The available data indicate that 20%–50% of the households in areas at risk continually monitor local news media as soon as a hurricane is within 72 h of possible landfall in their area. Moreover, this percentage rises to 60%–80% within 64 h of landfall and over 90% within 48 h of landfall. The data from hurricane studies are consistent with data from another slow-onset hazard (the arrival of the Indian Ocean tsunami in Mauritius) and a somewhat less severe hazard (the Boston water contamination incident). There appears to be no data on warning diffusion in hurricanes with late intensification or late-changing tracks. However, the available data on warning sources in these types of hurricanes suggest that the rates of diffusion of local evacuation warnings would be comparable to those in other rapid-onset events. [ABSTRACT FROM AUTHOR]

Tropomyosin and troponin regulate muscle contraction by participating in a macromolecular scale steric-mechanism to control myosin-crossbridge – actin interactions and consequently contraction. At low-Ca2+, the C-terminal 30% of troponin subunit-I (TnI) is proposed to trap tropomyosin in a position on thin filaments that sterically interferes with myosin-binding, thus causing muscle relaxation. In contrast, at high-Ca2+, inhibition is released after the C-terminal domains dissociate from F-actin-tropomyosin as its component switch-peptide domain binds to the N-lobe of troponin-C (TnC). Recent, paradigm-shifting, cryo-EM reconstructions by the Namba group have revealed density attributed to TnI along cardiac muscle thin filaments at both low- and high-Ca2+ concentration. Modeling the reconstructions showed expected high-Ca2+ hydrophobic interactions of the TnI switch-peptide and TnC. However, under low-Ca2+ conditions, sparse interactions of TnI and tropomyosin, and in particular juxtaposition of non-polar switch-peptide residues and charged tropomyosin amino acids in the published model seem difficult to reconcile with an expected steric-blocking conformation. This anomaly is likely due to inaccurate fitting of tropomyosin into the cryo-EM volume. In the current study, the low-Ca2+ cryo-EM volume was fitted with a more accurate tropomyosin model and representation of cardiac TnI. Our results show that at low-Ca2+ a cluster of hydrophobic residues at the TnI switch-peptide and adjacent H 4 helix (Ala149, Ala151, Met 154, Leu159, Gly160, Ala161, Ala163, Leu167, Leu169, Ala171, Leu173) draw-in tropomyosin surface residues (Ile143, Ile146, Ala151, Ile154), presumably attracting the entire tropomyosin cable to its myosin-blocking position on actin. The modeling confirms that neighboring TnI "inhibitory domain" residues (Arg145, Arg148) bind to thin filaments at actin residue Asp25, as previously suggested. ClusPro docking of TnI residues 137–184 to actin-tropomyosin, including the TnI inhibitory-domain, switch-peptide and Helix H 4 , verified the modeled configuration. Our residue-to-residue contact-mapping of the TnI-tropomyosin association lends itself to experimental validation and functional localization of disease-bearing mutations. [Display omitted] • The C-terminal 30% of TnI traps tropomyosin in the actin filament blocked-state. • This C-terminal TnI linkage to tropomyosin and actin relaxes muscle at low-Ca2+. • Our atomic model describes residue-to-residue TnI-actin-tropomyosin interaction. • The model provides a baseline map to understand TnI mutation-based imbalances. [ABSTRACT FROM AUTHOR]

Evaluating risk in first-degree relatives of patients diagnosed with hypertrophic cardiomyopathy (HCM) is a critical, ongoing clinical challenge, particularly when genetic testing yields a variant of unknown significance (VUS) in an HCM-related gene. Our goal is to develop a pipeline for efficient and scalable evaluation of VUS pathogenicity. Molecular dynamics simulations were used to screen twenty TPM1 VUS and identify four for further study: A102D, D258E, A239T, and K233N. Each VUS was engineered into an adenoviral TPM1 vector which was in turn applied to human engineered heart tissues (hEHTs) made from iPSC-derived cardiomyocytes. One week after viral exposure, isometric contractile behavior of hEHTs was measured. hEHTs expressing A102D were markedly hypercontractile, with a significant increase in contractile force and slowing of relaxation. D258E expression caused a mild phenotype, showing only a mildly increased relaxation rate relative to control. A238T and K233N both caused a dramatic decrease in contractile force. These same four VUS were studied in regulated in vitro motility assays and showed patterns of increased or decreased myofilament activity that were entirely consistent with findings in hEHT. A102D displayed a hypercontractile phenotype that resembled that of our benchmark HCM mutation (E62Q), while A238T and K233N produced contractile weakness that closely mimicked that of our benchmark DCM mutation (E54K). D258E had a minimal effect that could be interpreted as mildly hypertrophic. We conclude that hEHTs have the potential to serve as a scalable platform for evaluating pathogenicity of TPM1 VUS. [ABSTRACT FROM AUTHOR]

The role of private schools in this "mainstreaming" of the handicapped effort is outlined. (JMF)