Search

Defective genes account for ∼80% of the total of more than 7,000 diseases known to date. Gene therapy brings the promise of a one-time treatment option that will fix the errors in patient genetic coding. Recombinant viruses are highly efficient vehicles for in vivo gene delivery. Adeno-associated virus (AAV) vectors offer unique advantages, such as tissue tropism, specificity in transduction, eliciting of a relatively low immune responses, no incorporation into the host chromosome, and long-lasting delivered gene expression, making them the most popular viral gene delivery system in clinical trials, with three AAV-based gene therapy drugs already approved by the US Food and Drug Administration (FDA) or European Medicines Agency (EMA). Despite the success of AAV vectors, their usage in particular scenarios is still limited due to remaining challenges, such as poor transduction efficiency in certain tissues, low organ specificity, pre-existing humoral immunity to AAV capsids, and vector dose-dependent toxicity in patients. In the present review, we address the different approaches to improve AAV vectors for gene therapy with a focus on AAV capsid selection and engineering, strategies to overcome anti-AAV immune response, and vector genome design, ending with a glimpse at vector production methods and the current state of recombinant AAV (rAAV) at the clinical level.

The use of glyphosate-based herbicides is widespread and despite their extensive use, their effects are yet to be deciphered completely. The additives in commercial formulations of glyphosate, though labeled inert when used individually, have adverse effects when used in combination with other additives along with the active ingredient. As a species, Saccharomyces cerevisiae has a wide range of resistance to glyphosate-based herbicides. To investigate the underlying genetic differences between sensitive and resistant strains, global changes in gene expression were measured, when yeast were exposed to a glyphosate-based herbicide (GBH). Expression of genes involved in numerous pathways crucial to the cell’s functioning, such as DNA replication, MAPK signaling, meiosis, and cell wall synthesis changed. Because so many diverse pathways were affected, these strains were then subjected to in-lab-evolutions (ILE) to select mutations that confer increased resistance. Common fragile sites were found to play a role in adaptation to resistance to long-term exposure of GBHs. Copy number increased in approximately 100 genes associated with cell wall proteins, mitochondria, and sterol transport. Taking ILE and transcriptomic data into account it is evident that GBHs affect multiple biological processes in the cell. One such component is the cell wall structure which acts as a protective barrier in alleviating the stress caused by exposure to inert additives in GBHs. Sed1, a GPI-cell wall protein, plays an important role in tolerance of a GBH. Hence, a detailed study of the changes occurring at the genome and transcriptome levels is essential to better understand the effects of an environmental stressor such as a GBH, on the cell as a whole.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous cell population with high immunosuppressive activity that proliferates in infections, inflammation, and tumor microenvironments. In tumors, MDSC exert immunosuppression mainly by producing reactive oxygen species (ROS), a process triggered by the NADPH oxidase 2 (NOX2) activity. NOX2 is functionally coupled with the Hv1 proton channel in certain immune cells to support sustained free-radical production. However, a functional expression of the Hv1 channel in MDSC has not yet been reported. Here, we demonstrate that mouse MDSC express functional Hv1 proton channel by immunofluorescence microscopy, flow cytometry, and Western blot, besides performing a biophysical characterization of its macroscopic currents via patch-clamp technique. Our results show that the immunosuppression by MDSC is conditional to their ability to decrease the proton concentration elevated by the NOX2 activity, rendering Hv1 a potential drug target for cancer treatment.

SignificanceImmunosuppression by myeloid-derived suppressor cells (MDSC), especially near tumor surfaces, involves the extracellular production of reactive oxygen species (ROS). ROS generation in MDSC occurs during the oxidation of NADPH to NADP+, which NOX2 catalyzes. ROS react with the T cell receptor complex, abolishing the antigen presentation, which blocks the immune system elimination of the tumor cells. Extrusion of protons from MDSC by voltage-gated proton channel (Hv1) sustains ROS production. Here, we demonstrate the expression of Hv1 in mouse MDSC. In this way, Hv1 present in MDSC becomes a potential cancer therapeutic target since its inhibition seems to diminish immunosuppression activity in the tumoral microenvironment, allowing cancer cells to be attacked by the immune system.

Description, RECS1, a member of the TMBIM family, triggers lysosomal membrane permeabilization in cells undergoing lysosomal stress., Programmed cell death is regulated by the balance between activating and inhibitory signals. Here, we have identified RECS1 (responsive to centrifugal force and shear stress 1) [also known as TMBIM1 (transmembrane BAX inhibitor motif containing 1)] as a proapoptotic member of the TMBIM family. In contrast to other proteins of the TMBIM family, RECS1 expression induces cell death through the canonical mitochondrial apoptosis pathway. Unbiased screening indicated that RECS1 sensitizes cells to lysosomal perturbations. RECS1 localizes to lysosomes, where it regulates their acidification and calcium content, triggering lysosomal membrane permeabilization. Structural modeling and electrophysiological studies indicated that RECS1 is a pH-regulated calcium channel, an activity that is essential to trigger cell death. RECS1 also sensitizes whole animals to stress in vivo in Drosophila melanogaster and zebrafish models. Our results unveil an unanticipated function for RECS1 as a proapoptotic component of the TMBIM family that ignites cell death programs at lysosomes.

CACNA1I is implicated in the susceptibility to schizophrenia by large-scale genetic association studies of single nucleotide polymorphisms. However, the channelopathy of CACNA1I in schizophrenia is unknown. CACNA1I encodes CaV3.3, a neuronal voltage-gated calcium channel that underlies a subtype of T-type current that is important for neuronal excitability in the thalamic reticular nucleus and other regions of the brain. Here, we present an extensive functional characterization of 57 naturally occurring rare and common missense variants of CACNA1I derived from a Swedish schizophrenia cohort of more than 10 000 individuals. Our analysis of this allelic series of coding CACNA1I variants revealed that reduced CaV3.3 channel current density was the dominant phenotype associated with rare CACNA1I coding alleles derived from control subjects, whereas rare CACNA1I alleles from schizophrenia patients encoded CaV3.3 channels with altered responses to voltages. CACNA1I variants associated with altered current density primarily impact the ionic channel pore and those associated with altered responses to voltage impact the voltage-sensing domain. CaV3.3 variants associated with altered voltage dependence of the CaV3.3 channel and those associated with peak current density deficits were significantly segregated across affected and unaffected groups (Fisher’s exact test, P = 0.034). Our results, together with recent data from the SCHEMA (Schizophrenia Exome Sequencing Meta-Analysis) cohort, suggest that reduced CaV3.3 function may protect against schizophrenia risk in rare cases. We subsequently modelled the effect of the biophysical properties of CaV3.3 channel variants on thalamic reticular nucleus excitability and found that compared with common variants, ultrarare CaV3.3-coding variants derived from control subjects significantly decreased thalamic reticular nucleus excitability (P = 0.011). When all rare variants were analysed, there was a non-significant trend between variants that reduced thalamic reticular nucleus excitability and variants that either had no effect or increased thalamic reticular nucleus excitability across disease status. Taken together, the results of our functional analysis of an allelic series of >50 CACNA1I variants in a schizophrenia cohort reveal that loss of function of CaV3.3 is a molecular phenotype associated with reduced disease risk burden, and our approach may serve as a template strategy for channelopathies in polygenic disorders.

The Mediator is a multi-protein complex composed of subunits called head, body, tail, and CDK that is conserved from yeast to humans and plays a central role in transcription. However, not all the components are required for basal transcription. Components of the tail are not essential but to varying degrees are required for growth in different stresses. While some stresses are familiar such as heat, desiccation, and starvation, others are exotic, yet yeast can elicit a successful stress response. MCHM is a hydrotrope that induces growth arrest in yeast. By exploiting genetic variation, specifically in Med15, between yeast strains, we found that a naturally occurring Med15 allele with polyQ (polyglutamine) expansion conferred MCHM sensitivity. Expansion in polyQ repeat can induce protein aggregation and in humans can cause neurodegenerative diseases. In yeast, the MCHM sensitivity was not from a loss of function as the reciprocal hemizygous hybrids were all sensitive and the homozygous null mutant was less sensitive than the hemizygous hybrids. This suggests that there is an incompatibility between Mediator components from genetic divergent yeast strains. Transcriptomics from yeast expressing the incompatible Med15 (longer polyQ repeats in the strain with fewer repeats) changed gene expression in diverse pathways. Med15 protein existed in multiple isoforms, mostly from likely post-translational modifications and different alleles have different patterns of isoforms. Stability of both alleles of Med15 was dependent on Ydj1, a J-type chaperone. The protein level of the incompatible Med15 allele was lower than the compatible allele and was turned over faster. Med15 is tethered to the rest of the Mediator complex via Med2 and 3. Deletion of either Med2 or Med3 changed the Med15 isoform patterns in a similar manner. Whereas deletion of Med5, a distal component of the Mediator tail, did not change the pattern. The med2 and med3 mutants were similarly sensitive to MCHM while med5 mutants were not. Differences in the phenotype of yeast carrying different Med15 alleles extend to other stresses. The incompatible allele of Med15 improved growth of yeast to chemicals that produce free radicals and the compatible allele of Med15 improved growth to reducing agents, caffeine, and hydroxyurea. Med15 directly interacts with Gcn4 and other TFs and in vitro form phase-separated droplets. This variation may reflect the positive and negative role that Med15 has in transcription. Genetic variation in transcriptional regulators can magnify differences in response to environmental changes, in contrast, genetic variation in a metabolic enzyme. These polymorphic control genes are master variators.

While drugs and other industrial chemicals are routinely studied to assess risks, many widely used chemicals have not been thoroughly evaluated. One such chemical, 4-methylcyclohexane methanol (MCHM), is an industrial coal-cleaning chemical that contaminated the drinking water supply in Charleston, WV, USA in 2014. While a wide range of ailments was reported following the spill, little is known about the molecular effects of MCHM exposure. We used the yeast model to explore the impacts of MCHM on cellular function. Exposure to MCHM dramatically altered the yeast transcriptome and the balance of metals in yeast. Underlying genetic variation in the response to MCHM, transcriptomics and, mutant analysis uncovered the role of the metal transporters, Arn2 and Yke4, to MCHM response. Expression of Arn2, which is involved in iron uptake, was lower in MCHM-tolerant yeast and loss of Arn2 further increased MCHM tolerance. Genetic variation within Yke4, an ER zinc transporter, also mediated response to MCHM, and loss of Yke4 decreased MCHM tolerance. The addition of zinc to MCHM-sensitive yeast rescued growth inhibition. In vitro assays demonstrated that MCHM acted as a hydrotrope and prevented protein interactions, while zinc induced the aggregation of proteins. We hypothesized that MCHM altered the structures of extracellular domains of proteins, and the addition of zinc stabilized the structure to maintain metal homeostasis in yeast exposed to MCHM. Electronic supplementary material The online version of this article (10.1007/s12011-019-01850-z) contains supplementary material, which is available to authorized users.

Voltage-gated ion channels are the molecular determinants of cellular excitability. This group of ion channels is one of the most important pharmacological targets in excitable tissues such as nervous system, cardiac and skeletal muscle. Moreover, voltage-gated ion channels are expressed in non-excitable cells, where they mediate key cellular functions through intracellular biochemical mechanisms rather than rapid electrical signaling. This review aims at illustrating the pharmacological impact of these ion channels, highlighting in particular the structural details and physiological functions of two of them - the high conductance voltage- and Ca(2+)-gated K(+) (BK) channels and voltage-gated proton (Hv1) channels- in non-excitable cells. BK channels have been implicated in a variety of physiological processes ranging from regulation of smooth muscle tone to modulation of hormone and neurotransmitter release. Interestingly, BK channels are also involved in modulating K(+) transport in the mammalian kidney and colon epithelium with a potential role in the hyperkalemic phenotype observed in patients with familial hyperkalemic hypertension type 2, and in the pathophysiology of hypertension. In addition, BK channels are responsible for resting and stimulated Ca(2+)-activated K(+) secretion in the distal colon. Hv1 channels have been detected in many cell types, including macrophages, blood cells, lung epithelia, skeletal muscle and microglia. These channels have a central role in the phagocytic system. In macrophages, Hv1 channels participate in the generation of reactive oxygen species in the respiratory burst during the process of phagocytosis.

The main role of voltage-gated proton channels (Hv1) is to extrude protons from the intracellular milieu when, mediated by different cellular processes, the H+ concentration increases. Hv1 are exquisitely selective for protons and their structure is homologous to the voltage sensing domain (VSD) of other voltage-gated ion channels like sodium, potassium, and calcium channels. In clear contrast to the classical voltage-dependent channels, Hv1 lacks a pore domain and thus permeation necessarily occurs through the voltage sensing domain. Hv1 channels are activated by depolarizing voltages, and increases in internal proton concentration. It has been proposed that local conformational changes of the transmembrane segment S4, driven by depolarization, trigger the molecular rearrangements that open Hv1. However, it is still unclear how the electromechanical coupling is achieved between the VSD and the potential pore, allowing the proton flux from the intracellular to the extracellular side. Here we provide a revised view of voltage activation in Hv1 channels, offering a comparative scenario with other voltage sensing channels domains.

Carbon monoxide (CO) is a gaseous transmitter that is known to be involved in several physiological processes, but surprisingly it is also becoming a promising molecule to treat several pathologies including stroke and cancer. CO can cross the plasma membrane and activate guanylate cyclase, increasing the cGMP concentration and activating some kinases, including PKG. The other mechanism of action involves induction of protein carbonylation. CO is known to directly and indirectly modulate the function of ion channels at the plasma membrane, which in turn have important repercussions in the cellular behavior. One group of these channels is hemichannels, which are formed by proteins known as connexins (Cxs). Hemichannel allows not only the flow of ions through their pore but also the release of molecules such as ATP and glutamate. Therefore, their modulation not only impacts cellular function but also cellular communication, having the capability to affect tissular behavior. Here, we review the most recent results regarding the effect of CO on Cx hemichannels and their possible repercussions on pathologies. © 2015 IUBMB Life, 67(6):428–437, 2015

Being activated by depolarizing voltages and increases in cytoplasmic Ca(2+), voltage- and calcium-activated potassium (BK) channels and their modulatory β-subunits are able to dampen or stop excitatory stimuli in a wide range of cellular types, including both neuronal and nonneuronal tissues. Minimal alterations in BK channel function may contribute to the pathophysiology of several diseases, including hypertension, asthma, cancer, epilepsy, and diabetes. Several gating processes, allosterically coupled to each other, control BK channel activity and are potential targets for regulation by auxiliary β-subunits that are expressed together with the α (BK)-subunit in almost every tissue type where they are found. By measuring gating currents in BK channels coexpressed with chimeras between β1 and β3 or β2 auxiliary subunits, we were able to identify that the cytoplasmic regions of β1 are responsible for the modulation of the voltage sensors. In addition, we narrowed down the structural determinants to the N terminus of β1, which contains two lysine residues (i.e., K3 and K4), which upon substitution virtually abolished the effects of β1 on charge movement. The mechanism by which K3 and K4 stabilize the voltage sensor is not electrostatic but specific, and the α (BK)-residues involved remain to be identified. This is the first report, to our knowledge, where the regulatory effects of the β1-subunit have been clearly assigned to a particular segment, with two pivotal amino acids being responsible for this modulation.

The functional dichotomy of antibodies against interleukin-2 (IL-2) is thought to depend upon recognition of different cytokine epitopes. Beyond functional studies, the only molecular evidence obtained so far located the epitopes recognized by the immunoenhancing antibodies S4B6 and JES6–5H4 within the predicted interface of IL-2 with the α receptor subunit, explaining the preferential stimulation of effector cells displaying only β and γ receptor chains. A consistent functional map of the epitope bound by the immunoregulatory antibody JES6-1A12 has now been delineated by screening the interactions of phage-displayed antigen variants (with single and multiple mutations) and antigen mimotopes. The target determinant resides in a region between the predicted interfaces with α and β/γ receptor subunits, supporting the dual inhibitory role of the antibody on both interactions. Binding by JES6-1A12 would thus convert complexed IL-2 into a very weak agonist, reinforcing the advantage of T regulatory cells (displaying the high affinity αβγ heterotrimeric receptor) to capture the cytokine by competition and expand over effector cells, ultimately resulting in the observed strong tolerogenic effect of this antibody. Detailed knowledge of the epitopes recognized by anti-IL-2 antibodies with either immunoenhancing or immunoregulatory properties completes the molecular scenario underlying their use to boost or inhibit immune responses in multiple experimental systems. The expanded functional mapping platform now available could be exploited to study other interactions involving related molecular pairs with the final goal of optimizing cytokine and anti-cytokine therapies.

P3 is a murine, germline, IgM mAb that recognizesN-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VHregion was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens.

Elucidating the network of interactions established by Interleukin-2 is a key step to understanding its role as a master regulator of the immune system. Binding of this cytokine by specific antibodies gives rise to different classes of immune complexes that boost or inhibit immune responses. The molecular bases of such functional dichotomy are likely related to the nature of the recognized epitopes, making it necessary to perform fine epitope mapping studies. The current work was aimed at developing a versatile platform to do so. This was accomplished by display of human and mouse Interleukin-2 on filamentous phages, together with extensive mutagenesis of both antigens and high throughput screening of binding properties of more than 200 variants. Detailed molecular pictures of the epitopes were thus delineated for four antibodies against either human or mouse Interleukin-2, which refined and, in some cases, modified the conclusions derived from previous mapping studies with peptide libraries. Overlapping surface patches on mouse Interleukin-2 that also coincide with the predicted interface between the cytokine and its receptor alpha chain were shown to be recognized by two monoclonal antibodies that promote enhancement of immune responses, shedding new light on the structural bases of their biological activity. Our strategy was powerful enough to reveal multiple binding details and could be used to map the epitopes recognized by other antibodies and to explore additional interactions involving Interleukin-2 and related cytokines, thus contributing to our understanding of the complex structure–function relationships within the immune system.

The opening of connexin (Cx) hemichannels in the membrane is tightly regulated by calcium (Ca2+) and membrane voltage. Electrophysiological and atomic force microscopy experiments indicate that Ca2+ stabilizes the hemichannel closed state. However, structural data show that Ca2+ binding induces an electrostatic seal preventing ion transport without significant structural rearrangements. In agreement with the closed-state stabilization hypothesis, we found that the apparent Ca2+ sensitivity is increased as the voltage is made more negative. Moreover, the voltage and Ca2+ dependence of the channel kinetics indicate that the voltage sensor movement and Ca2+ binding are allosterically coupled. An allosteric kinetic model in which the Ca2+ decreases the energy necessary to deactivate the voltage sensor reproduces the effects of Ca2+ and voltage in Cx46 hemichannels. In agreement with the model and suggesting a conformational change that narrows the pore, Ca2+ inhibits the water flux through Cx hemichannels. We conclude that Ca2+ and voltage act allosterically to stabilize the closed conformation of Cx46 hemichannels.

P3 is a murine, germline, IgM mAb that recognizes N-glycolylated gangliosides and other self-antigens. This antibody is able to induce an anti-idiotypic IgG response and B-T idiotypic cascade, even in the absence of any adjuvant or carrier protein. P3 mAb immunization induces the expression of activation markers in a significant percentage of B-1a cells in vivo. Interestingly, transfer of both B-1a and B-2 to BALB/Xid mice was required to recover anti-P3 IgG response in this model. In fact, P3 mAb activated B-2 cells, in vitro, inducing secretion of IFN-γ and IL-4, although this activation was not detected ex vivo. Interestingly, naïve CD8+ T cells increased the expression of activation markers and IFN-γ secretion in the presence of B-1a cells isolated from P3 mAb-immunized mice, even without in vitro restimulation. In contrast, B-2 cells were able to stimulate CD8+ T cells only if P3 was added in vitro. Using bioinformatics, a MHC class I-binding peptide from P3 VH region was identified. P3 mAb was able to induce a specific CTL response in vivo against cells presenting this peptide. Both humoral and CTL anti-idiotypic responses could be mechanisms to protect against the self-reactive antibody, contributing to keeping the tolerance to self-antigens.

Rotamer libraries are collections of side-chain conformations compiled for each type of amino acid. All the libraries developed so far were constructed based on different sets of proteins, none of which includes small peptidic molecules. Are the existing rotamer libraries suitable for modeling the side chains of peptidic ligands in complex with their receptors? To answer this question, we have tested 10 different, publicly available and commonly used rotamer libraries for their capability of reproducing the side-chain conformations (and therefore the receptor-ligand interactions) of hundreds of short peptidic ligands found in the Protein Data Bank, including large sets of class I and class II T-cell epitopes. Only the libraries developed by Xiang and Honig were able to correctly reproduce the experimental geometries for most of the analyzed residues, and the atomic interactions between the peptidic ligands and their receptors. Surprisingly, all the libraries showed a lower performance in reproducing the side chains conformations from structures solved at very high resolution (R

Plasmepsins are aspartic proteases involved in the initial steps of the hemoglobin degradation pathway, a critical stage in the Plasmodium falciparum life cycle during human infection. Thus, they are attractive targets for novel therapeutic compounds to treat malaria, which remains one of the world's biggest health problems. The three-dimensional structures available for P. falciparum plasmepsins II and IV make structure-based drug design of antimalarial compounds that focus on inhibiting plasmepsins possible. However, the structural flexibility of the plasmepsin active site cavity combined with insufficient knowledge of the functional residues and of those determining the specificity of parasitic enzymes is a drawback when designing specific inhibitors. In this study, we have combined a sequence and structural analysis with molecular dynamics simulations to predict the functional residues in P. falciparum plasmepsins. The careful analysis of X-ray structures and 3D models carried out here suggests that residues Y17, V105, T108, L191, L242, Q275, and T298 are important for plasmepsin function. These seven amino acids are conserved across the malarial strains but not in human aspartic proteases. Residues V105 and T108 are localized in a flap of an interior pocket and they only establish contacts with a specific non-peptide achiral inhibitor. We also observed a rapid conformational change in the L3 region of plasmepsins that closes the active site of the enzyme, which explains earlier experimental findings. These results shed light on the role of V105 and T108 residues in plasmepsin specificities, and they should be useful in structure-based design of novel, selective inhibitors that may serve as antimalarial drugs. Proteins 2008. © 2008 Wiley-Liss, Inc.

The pharmacological modulation of the immunosuppressive tumor microenvironment has emerged as a relevant component for cancer therapy. Several approaches aiming to deplete innate and adaptive suppressive populations, to circumvent the impairment in antigen presentation, and to ultimately increase the frequency of activated tumor-specific T cells are currently being explored. In this review, we address the potentiality of targeting the voltage-gated proton channel, Hv1, as a novel strategy to modulate the tumor microenvironment. The function of Hv1 in immune cells such as macrophages, neutrophils, dendritic cells, and T cells has been associated with the maintenance of NADPH oxidase activity and the generation of reactive oxygen species, which are required for the host defense against pathogens. We discuss evidence suggesting that the Hv1 proton channel could also be important for the function of these cells within the tumor microenvironment. Furthermore, as summarized here, tumor cells express Hv1 as a primary mechanism to extrude the increased amount of protons generated metabolically, thus maintaining physiologic values for the intracellular pH. Therefore, because this channel might be relevant for both tumor cells and immune cells supporting tumor growth, the pharmacological inhibition of Hv1 could be an innovative approach for cancer therapy. With that focus, we analyzed the available compounds that inhibit Hv1, highlighted the need to develop better drugs suitable for patients, and commented on the future perspectives of targeting Hv1 in the context of cancer therapy.

Several mutations in Cx26 promote keratitis ichthyosis deafness (KID), a rare disease in which patients exhibit deafness, skin and corneal disorders. Some KID mutations are located in the amino terminal segment of Cx26, which has been proposed as the putative voltage sensor. Most syndromic mutations elicit a gain of hemichannel function, however the mechanism underlying this phenomenon remains unclear. Here we examined the biophysical properties of the mutant G12R at macroscopic and single channel levels. We perform two-electrode voltage clamp to study the deactivation kinetics and apparent affinity for calcium of hemichannel currents. In contrast to wild-type (wt) Cx26, we found that the activation kinetics of the mutant lack saturation of the current upon depolarization pulses above +40 mV. Estimates of the deactivation time constant yield values of 5s and 10s for G12R and wtCx26 hemichannels, respectively; however the apparent affinity for calcium remains similar to wtCx26. Single channel recordings analysis showed that the mutant virtually eliminates the transitions to the subconductance state. Moreover, although the single channel conductance was similar to wtCx26 hemichannels (320 pS), the open probability and mean open times of G12R hemichannels become larger. Molecular dynamics indicates that the G12R induce an electrostatic effect and ddG calculations support protein destabilization.Supported by Fondecyt-3150634 to IEG; Fondecyt-3140590 to GC; Fondecyt-1130855 to ADM; Anillo-ACT1104 to ADM and CG; Fondecyt-1120802 to CG; Grant RO1-GM099490 to J.E.C; AP has a Conicyt Fellowship. The Centro Interdisciplinario de Neurociencias de Valparaiso is a Chilean Millennium Institute (P09-022-F).

Indexación: Scopus. Connexin-based channels comprise hemichannels and gap junction channels. The opening of hemichannels allow for the flux of ions and molecules from the extracellular space into the cell and vice versa. Similarly, the opening of gap junction channels permits the diffusional exchange of ions and molecules between the cytoplasm and contacting cells. The controlled opening of hemichannels has been associated with several physiological cellular processes; thereby unregulated hemichannel activity may induce loss of cellular homeostasis and cell death. Hemichannel activity can be regulated through several mechanisms, such as phosphorylation, divalent cations and changes in membrane potential. Additionally, it was recently postulated that redox molecules could modify hemichannels properties in vitro. However, the molecular mechanism by which redox molecules interact with hemichannels is poorly understood. In this work, we discuss the current knowledge on connexin redox regulation and we propose the hypothesis that extracellular cysteines could be important for sensing changes in redox potential. Future studies on this topic will offer new insight into hemichannel function, thereby expanding the understanding of the contribution of hemichannels to disease progression. http://journal.frontiersin.org/article/10.3389/fphys.2016.00001/full

Connexins (Cxs) are a family of membrane-spanning proteins that form gap junction channels and hemichannels. Connexin-based channels exhibit two distinct voltage-dependent gating mechanisms termed slow and fast gating. Residues located at the C terminus of the first transmembrane segment (TM-1) are important structural components of the slow gate. Here, we determined the role of the charged residues at the end of TM-1 in voltage sensing in Cx26, Cx46, and Cx50. Conductance/voltage curves obtained from tail currents together with kinetics analysis reveal that the fast and slow gates of Cx26 involves the movement of two and four charges across the electric field, respectively. Primary sequence alignment of different Cxs shows the presence of well conserved glutamate residues in the C terminus of TM-1; only Cx26 contains a lysine in that position (lysine 41). Neutralization of lysine 41 in Cx26 increases the voltage dependence of the slow gate. Swapping of lysine 41 with glutamate 42 maintains the voltage dependence. In Cx46, neutralization of negative charges or addition of a positive charge in the Cx26 equivalent region reduced the slow gate voltage dependence. In Cx50, the addition of a glutamate in the same region decreased the voltage dependence, and the neutralization of a negative charge increased it. These results indicate that the charges at the end of TM-1 are part of the slow gate voltage sensor in Cxs. The fact that Cx42, which has no charge in this region, still presents voltage-dependent slow gating suggests that charges still unidentified also contribute to the slow gate voltage sensitivity.

The keratitis-ichthyosis-deafness (KID) syndrome is characterized by corneal, skin, and hearing abnormalities. KID has been linked to heterozygous dominant missense mutations in the GJB2 and GJB6 genes, encoding connexin26 and 30, respectively. In vitro evidence indicates that KID mutations lead to hyperactive (open) hemichannels, which in some cases is accompanied by abnormal function of gap junction channels. Transgenic mouse models expressing connexin26 KID mutations reproduce human phenotypes and present impaired epidermal calcium homeostasis and abnormal lipid composition of the stratum corneum affecting the water barrier. Here we have compiled relevant data regarding the KID syndrome and propose a mechanism for the epidermal aspects of the disease.

Sticholysins I and II (Sts I and II) are two potent cytolysins from the sea anemone Stichodactyla helianthus. These isoforms present 13 substitutions, with three non-conservative located at the N-terminus. St II is considerably more hemolytic than St I in human red blood cells, a result explained by the smaller number of negatively charged groups present at St II's N-terminus. In the present work, we have obtained a recombinant St I (rSt I), differing from the wild type in a single amino acid residue (E16Q). This pseudo-wild type is structurally similar to St I and shows a similar capacity to interact with and form pores in model membranes. This was assessed by the intrinsic fluorescence increase in the presence of liposomes, their adsorption to bilayers (measured by SPR), their concentration at the air-water interface, their interaction with lipid monolayers and their capacity to promote the release of carboxyfluorescein entrapped in liposomes. In spite of these similarities, rSt I presents a larger hemolytic activity in human red blood cells than St I, being intermediate in activity between Sts I and II. The results obtained in the present work emphasize that even the change of one single E by Q at the N-terminal segment may modify the toxin HA and show that this functional property is the most sensitive to subtle changes in the protein primary structure.

The voltage-gated proton channel (Hv1) is a dimer of subunits containing four transmembrane domains (S1-S4) which play the double role of harboring the voltage-sensing charges and forming the proton conduction pathway. Some biophysical properties of Hv1

Carbon monoxide (CO) is a gaseous transmitter that is known to be involved in several physiological processes, but surprisingly it is also becoming a promising molecule to treat several pathologies including stroke and cancer. CO can cross the plasma membrane and activate guanylate cyclase, increasing the cGMP concentration and activating some kinases, including PKG. The other mechanism of action involves induction of protein carbonylation. CO is known to directly and indirectly modulate the function of ion channels at the plasma membrane, which in turn have important repercussions in the cellular behavior. One group of these channels is hemichannels, which are formed by proteins known as connexins (Cxs). Hemichannel allows not only the flow of ions through their pore but also the release of molecules such as ATP and glutamate. Therefore, their modulation not only impacts cellular function but also cellular communication, having the capability to affect tissular behavior. Here, we review the most recent results regarding the effect of CO on Cx hemichannels and their possible repercussions on pathologies.

The most well-known role of Connexins (Cxs) is to communicate the cytoplasm of two adjacent cells forming a gap junction channel in the apposition zone. On the other hand, Cxs form the so called “hemichannels”, a fully functional voltage-gated non-selective ion channel, which present two gating mechanism called “slow” and “fast” gating. Hemichannels consist of 6 monomers, each one composed of four transmembrane domains. Despite the fact that hemichannels are voltage-activated, they lack the classical voltage-sensing domain described for canonical voltage-gated channels. Furthermore, the molecular determinants associated to the voltage activation in connexins hemichannels are still elusive. In this work we search for the molecular determinants associated to voltage detection in human Cx26 hemichannels. Using two electrode voltage-clamp in Xenopus laevis oocytes, we study how the steady-state conductance-voltage (G/V) relationship and kinetics of gating are affected by the neutralization of different charged residues located within the first transmembrane domain. We have found that Cx26 conductance-voltage curve shows an apparent number of gating charges (zδ) of 1.4 e0 for the slow gating mechanism. On the other hand, we obtained a zδ of 3.9 e0 for the fast gate, which is in agreement with the zδ of Cx26 gap junctions. A simple three-state closed-open1-open2 kinetic model is able to account for the channel voltage dependence. Furthermore, our data shows that neutralizing the K41 residue (K41N) increases the zδ; of the slow gate to 2.5 e0, and decreases the zδ of the fast gate to 2.3 e0.This work is supported by FONDECYT Grants 1110430 (R.L.), 1120802 (C.G.), 1130855 (A.M.); ANILLO Grant ACT1104 (C.G.); Beca para Estudios de Magister en Chile Ano 2014 (B.P.); CINV is a Millennium Institute supported by the Millennium Scientific Initiative of the Ministerio de Economia, Fomento y Turismo.

Molecular details of epidermal growth factor receptor (EGFR) targeting by nimotuzumab, a therapeutic anti-cancer antibody, have been largely unknown. The current study delineated a functional map of their interface, based on phage display and extensive mutagenesis of both the target antigen and the Fv antibody fragment. Five residues in EGFR domain III (R353, S356, F357, T358, and H359T) and the third hypervariable region of nimotuzumab heavy chain were shown to be major functional contributors to the interaction. Fine specificity differences between nimotuzumab and other anti-EGFR antibodies were revealed. Mapping information guided the generation of a plausible in silico binding model. Knowledge about the epitope/paratope interface opens new avenues for the study of tumor sensitivity/resistance to nimotuzumab and for further engineering of its binding site. The developed mapping platform, also validated with the well-known cetuximab epitope, allows a comprehensive exploration of antigenic regions and could be expanded to map other anti-EGFR antibodies.

Although multiple different procedures to characterize the epitopes recognized by antibodies have been developed, site-directed mutagenesis remains the method of choice to define the energetic contribution of antigen residues to binding. These studies are useful to identify critical residues and to delineate functional maps of the epitopes. However, they tend to underestimate the roles of residues that are not critical for binding on their own, but contribute to the formation of the target epitope in an additive, or even cooperative, way. Mapping antigenic determinants with a diffuse energetic landscape, which establish multiple individually weak interactions with the antibody paratope, resulting in high affinity and specificity recognition of the epitope as a whole, is thus technically challenging. The current work was aimed at developing a combinatorial strategy to overcome the limitations of site-directed mutagenesis, relying on comprehensive randomization of discrete antigenic regions within phage-displayed antigen libraries. Two model antibodies recognizing epidermal growth factor were used to validate the mapping platform. Abrogation of antibody recognition due to the introduction of simultaneous replacements was able to show the involvement of particular amino acid clusters in epitope formation. The abundance of some of the original residues (or functionally equivalent amino acids sharing their physicochemical properties) among the set of mutated antigen variants selected on a given antibody highlighted their contributions and allowed delineation of a detailed functional map of the corresponding epitope. The use of the combinatorial approach could be expanded to map the interactions between other antigens/antibodies.

Voltage-gated proton channels are integral membrane proteins with the capacity to permeate elementary particles in a voltage and pH dependent manner. These proteins have been found in several species and are involved in various physiological processes. Although their primary topology is known, lack of details regarding their structures in the open conformation has limited analyses toward a deeper understanding of the molecular determinants of their function and regulation. Consequently, the function-structure relationships have been inferred based on homology models. In the present work, we review the existing proton channel models, their assumptions, predictions and the experimental facts that support them. Modeling proton channels is not a trivial task due to the lack of a close homolog template. Hence, there are important differences between published models. This work attempts to critically review existing proton channel models toward the aim of contributing to a better understanding of the structural features of these proteins.

We have previously reported the isolation of a novel single-chain variable fragment (scFv) against vascular endothelial growth factor (VEGF), from a phage-displayed human antibody repertoire. This scFv, denominated 2H1, was shown to block the binding of VEGF to its receptor but exhibited a moderate binding affinity. Here, we describe the affinity maturation of the 2H1 scFv. Two phage-displayed libraries were constructed by diversification of the third complementarity-determining regions (CDRs) of the light (VL) and heavy (VH) chain variable domains of 2H1 using parsimonious mutagenesis. A competitive phage-selection strategy in the presence of the parental scFv as a competitor was used to eliminate low affinity binders. High affinity variants were retrieved from both libraries. An optimized VL variant was designed and constructed by combining recurrent replacements found among selected variants in a single molecule, resulting in an additional affinity increase. Further affinity improvements were achieved by combining this optimized VL with the best VH variants. The final variant obtained here, L3H6, showed an overall affinity improvement of 18-fold over the parental scFv and exhibited an enhanced potency to block the binding of VEGF to its receptor. Using phage display and extensive mutagenesis of VEGF, we determined the fine specificity of L3H6. This functional mapping revealed a novel neutralizing epitope on human VEGF defined by the residues Y25, T71, E72, N100, K101, E103 and R105. The conformational epitope recognized by L3H6 was recapitulated by grafting human VEGF residues into the mouse molecule, providing further confirmation of the nature of the identified epitope.

Connexins (Cxs) are transmembrane proteins involved in the electrical coupling of cells, the release of signaling molecules, and cell proliferation among others. These proteins are expressed in almost every tissue of the human body and mutations in these proteins are related to several hereditary diseases. Cxs monomers oligomerize in hexamers, which traffic to the plasma membrane and form connexons or hemichannels that can act as plasma membrane channels or can travel to intercellular contact zones where they form intercellular channels known as gap junctions. The opening of the Cx hemichannels in the membrane is tightly regulated by Ca2+ and membrane voltage. This regulation prevents leakage of cellular content and its malfunction may lead to pathologic conditions. In this work we studied the reciprocal regulation of Cxs hemichannels by Ca2+ and voltage. We expressed Cx46 in Xenopus laevis oocytes, and using two electrode voltage clamp, analyzed the inhibition of currents by Ca2+. We observed that Cxs inhibition by Ca2+ is voltage dependent. The apparent Ca2+ sensitivity is increased as the membrane voltage is made more negative. This change in the affinity can be explained by a stabilization of the closed state of the Cx channel by Ca2+. We propose a model in which the calcium-bonded state prevents the opening of the hemichannel. The model allows us to determine the affinity of the closed state for calcium. In agreement with the model and suggesting a stabilization of a conformational change that narrows the pore, calcium inhibits the water flux trough Cx hemichannels. This work supports the idea that Ca2+ and voltage act synergistically to promote the closing of the pore in Cx channels.

Parallel ligand- and structure-based virtual screenings of 269 steroids with anabolic activity evaluated in vivo were performed. The quantitative structure-activity relationship (QSAR) model expressed by selected descriptors as the octanol-water partition coefficient, the molar volume and the quantum mechanical calculated charge values on atoms C1, C2, C5, C9, C10, C14 and C17 of the steroid skeleton, expresses structural features of anabolic steroids (AS) contributing to the transport and steroid-receptor interaction. On the other hand, computational simulations of a candidate ligand binding to a receptor study (a "docking" procedure) predict the association of these AS with the human androgen receptor (AR). Fourteen compounds were identified as lead; the most potent was the 7α-methylestr-4-en-3, 17-dione. It was concluded that a good anabolic activity requires hydrogen bonding interactions between both Arg752 and Gln711 residues in the cycles A with O3 atom of the steroid and either Asn705 and Thr877 residues in the cycles D of steroid with O17 atom.

The structurally related gangliosides N-glycolyl GM3 and N-acetyl GM3 are potential targets for tumor immunotherapy. 14F7 is a monoclonal antibody able to discriminate the tumor-specific antigen N-glycolyl GM3 from the closely related N-acetyl GM3 on the basis of the presence of a single additional hydroxyl group in the former. A combinatorial phage display strategy, based on the screening of a large library followed by refined mutagenesis, allowed a thorough exploration of the binding chemistry of this unique antibody. Three essential features of the heavy chain variable region were identified: two aromatic rings (in positions 33 and 100D) contributing to the binding site architecture and an arginine residue (position 98) critical for recognition. Directed evolution of 14F7 resulted in novel variants that cross-react with the tumor-associated antigen N-acetyl GM3 and display recurrent replacements: the substitution W33Q and the appearance of additional arginine residues at several positions of CDR H1. Successful conversion of such engineered variable regions into whole cross-reactive anti-GM3 immunoglobulins validated our phage-based approach to study and modify the lead antibody 14F7. The resulting family of closely related antibodies offers new tools to study the mechanisms of cell death induced by antibodies targeting gangliosides. In vitro directed evolution was useful to overcome the technical limitations to obtain anti-ganglioside antibodies. The case of 14F7 illustrates the power of combining library screening with focused site-directed randomization for a comprehensive scanning of protein interactions.

Of the ∼22,000 protein-coding genes in the human genome, an estimated 8,000 are druggable (1). The current drug market targets no more than 450 unique human proteins (1) and many contain antihypertensive, antineoplastic, or anti-inflammatory effects. Receptors, enzymes, and transporter proteins comprise most of the targets. The following protein families are overrepresented: rhodopsin-like G protein-coupled receptors, voltage-gated ion channels, and ligand-gated ion channels (1). Their membrane localization, diverse tissue distribution, and the critical roles played by ion channels in human physiology makes these proteins attractive targets for drug discovery (2). Although worldwide sales of ion channel-targeted drugs are over US$10 billion, ion channels remain significantly underexploited as therapeutic targets (3).

Overexpression of the epidermal growth factor (EGF) receptor (EGFR) in cancer cells correlates with tumor malignancy and poor prognosis for cancer patients. For this reason, the EGFR has become one of the main targets of anticancer therapies. Structural data obtained in the last few years have revealed the molecular mechanism for ligand-induced EGFR dimerization and subsequent signal transduction, and also how this signal is blocked by either monoclonal antibodies or small molecules. Nimotuzumab (also known as h-R3) is a humanized antibody that targets the EGFR and has been successful in the clinics. In this work, we report the crystal structure of the Fab fragment of Nimotuzumab, revealing some unique structural features in the heavy variable domain. Furthermore, competition assays show that Nimotuzumab binds to domain III of the extracellular region of the EGFR, within an area that overlaps with both the surface patch recognized by Cetuximab (another anti-EGFR antibody) and the binding site for EGF. A computer model of the Nimotuzumab-EGFR complex, constructed by docking and molecular dynamics simulations and supported by mutagenesis studies, unveils a novel mechanism of action, with Nimotuzumab blocking EGF binding while still allowing the receptor to adopt its active conformation, hence warranting a basal level of signaling. [Cancer Res 2009;69(14):5851–9]

Phage-displayed peptides recognized by two monoclonal antibodies against glucitollysine were selected. The most prominent feature of the peptide panel was the presence of paired Cys in most of them (21/24 peptides). The availability of a wide variety of peptides having differently spaced paired Cys, as well as truly linear Cys-free peptides, gave the opportunity to explore the role of disulfide bridges in phage selection. Some Cys-containing peptides came from a Cys-flanked cyclic 9-mer library, but most of them (18/21) were derived from a totally random 12-mer library, and hence the presence of Cys was dictated by the selector antibodies. Motifs shared by several peptides (potentially involved in binding) often contained or were flanked by Cys residues. Binding of all Cys-containing phage-displayed peptides was abolished/decreased after a reducing treatment. Screening a random peptide library (without invariant Cys residues) is powerful enough to clearly reveal the need, preferences, and diversity of Cys-mediated structural constraints for recognition.

Hv1 channels are integral membrane proteins with the capacity to selectively permeate protons in a voltage and pH-dependent manner. As Hv1 lacks a pore domain, permeation must occur through the voltage-sensing domain. Previous reports propose a permeation pathway consisting in a stable water wire which allows proton to permeate by means of a Grotthuss mechanism. Our molecular dynamics simulations do not support the formation of such stable water wire since it shows a dry zone around residue N264 in the wild type and in N264 mutants. Mutations of residues D222 and N264 affects single channel conductance (determined by non-stationary noise analysis) and selectivity, suggesting that both residues are involved in the permeation pathway. Quantum dynamics simulations performed in our model of the open Ci-Hv1 wt and in silico mutants suggest that permeation occur through a proton wire involving residues D160 and D222, a process modulated by N264.Supported by Beca de Doctorado Nacional para Extranjeros de Conicyt (A.P), FONDECYT Grants 1110430 (R.L.), 1120802 (C.G.); ANILLO Grant ACT1104 (C.G.); Postdoctoral Fellowships 3140590 (G.F.C.). CINV is a Millennium Institute.