Biology subjects

Cail, R. C.

Publications and source records attributed to Cail, R. C..

5 recordsLinked to original sources

bioRxiv2025

A myosin hypertrophic cardiomyopathy mutation disrupts the super-relaxed state and boosts contractility by enhanced actin attachment

Hypertrophic cardiomyopathy (HCM) is a leading cause of cardiac failure among individuals under 35. Many genetic mutations that cause HCM enhance ventricular systolic function, suggesting that these HCM mutations are hypercontractile. Among the most common causes of HCM are mutations in the gene MYH7, which encodes for {beta}-cardiac myosin, the principal human ventricular myosin. Previous work has demonstrated that, for purified myosins, some MYH7 mutations are gain-of-function while others cause reduced function, so how they lead to enhanced contractility is not clear. Here, we have characterized the mechanics and kinetics of the severe HCM-causing mutation M493I. Motility assays demonstrate a 70% reduction of actin filament gliding velocities on M493I-coated surfaces relative to WT. This mutation slows ADP release from actomyosin{middle dot}ADP 5-fold without affecting phosphate release or ATP binding. Yet it enhances steady-state ATPase Vmax 2-fold. Through single-molecule mechanical studies, we find that M493I myosin has a normal working stroke of 5 nm but a significantly prolonged actin attachment duration. Under isometric feedback, M493I myosins produce high, sustained force, with an actin detachment rate that is less sensitive to force than that of WT myosin. We also report direct measurement of the equilibrium state of the super-relaxed to disordered relaxed (SRX-DRX) regulatory transition and show its disruption in M493I, with a concomitant enhancement to actin attachment kinetics. Together, these data demonstrate that enhanced myosin binding from inhibition of myosins off state, combined with slow ADP release and enhanced force production, underlie the enhanced function and etiology of this HCM mutation. Significance StatementHypertrophic cardiomyopathy (HCM) is a leading genetic cause of sudden cardiac death in young individuals. Although often described as a hypercontractile disease, the molecular basis for this remains unclear, especially for mutations with inhibitory effects in various in vitro assays. We show that the severe HCM mutation M493I in {beta}-cardiac myosin slows ADP release yet enhances force output and actin attachment through multiple mechanisms, including disrupted autoinhibition via the super-relaxed state. Our findings unify seemingly contradictory biophysical changes into a coherent mechanistic model and support the hypothesis that increased myosin head availability, rather than enhanced individual kinetics alone, underlies HCM hypercontractility.

biophysics↗

bioRxiv2025

S2Tag, a novel affinity tag for the capture and immobilization of coiled-coil proteins: application to the study of human β-cardiac myosin

Single molecule and ensemble motility assays are powerful tools for investigating myosin activity. A key requirement for the quality and reproducibility of the data obtained with these methods is the mode of attachment of myosin to assay surfaces. We previously characterized the ability of a monoclonal antibody (10F12.3) to tether skeletal muscle myosin to nitrocellulose coated glass. Here, we identify the 11 amino-acid epitope (S2Tag) recognized by 10F12.3 in the coiled-coil S2 domain of myosin. To test the transferability of S2Tag, we inserted it into a wild-type {beta}-cardiac myosin construct (WT-{beta}CM) and evaluated its mechanochemistry. WT-{beta}CM immobilized via S2Tag robustly propelled actin filaments in gliding assays and showed single-molecule actin displacements and attachment kinetics by optical trapping. Thus, the antibody attachment is effective for ensemble and single molecule assays. We inserted the S2Tag into a {beta}CM construct containing a penetrant mutation (S532P-{beta}CM) that causes dilated cardiomyopathy. Inclusion of S2Tag enabled quantitative mixed-motor gliding filament assays with WT-{beta}CM. The analysis shows the S532P mutation results in a 60% decrease in gliding speed, yet the motor seems to produce the same force as WT-{beta}CM. Importantly, S2Tag is a useful new tool for affinity capture of alpha-helical coiled coil proteins.

biophysics↗

bioRxiv2024

Dynamics of β-cardiac myosin between the super-relaxed and disordered-relaxed states

The super-relaxed (SRX) state of myosin ATPase activity is critical for striated muscle function, and its dysregulation is linked to cardiomyopathies. It is unclear whether the SRX state exchanges readily with the disordered-relaxed (DRX) state, and whether the SRX state directly corresponds to the folded back interacting-head motif (IHM). Using recombinant {beta}-cardiac heavy meromyosin (HMM) and subfragment 1 (S1), which cannot form the IHM, we show that the SRX and DRX populations are in rapid equilibrium, dependent on myosin head-tail interactions. Some mutations which cause hypertrophic (HCM) or dilated (DCM) cardiomyopathies alter the SRX-DRX equilibrium, but not all mutations. The cardiac myosin inhibitor mavacamten slows nucleotide release by an equal factor for both HMM and S1, thus only indirectly influencing the occupancy time of the SRX state. These findings suggest that purified myosins undergo rapid switching between SRX and DRX states, refining our understanding of cardiomyopathy mechanisms.

biochemistry↗

bioRxiv2021

Induced Membrane Curvature Bypasses Clathrin's Essential Endocytic Function

During membrane trafficking, flat membrane is rapidly remodeled to produce nanometer-scale vesicles. The mechanisms underlying this shape change are not completely understood, but coat proteins such as clathrin are implicated. Clathrins ability to bind to membranes of many different geometries casts uncertainty on its specific role in curvature generation and stabilization. Here, we used nanopatterning to produce substrates of ideal optical properties for live-cell imaging, with U-shaped features that bend a cells ventral plasma membrane into shapes characteristic of the energetically-unfavorable intermediate of clathrin- mediated endocytosis (CME). This induced plasma membrane curvature recruits the endocytic machinery, promoting productive endocytosis. Upon clathrin or AP2 disruption, CME sites on flat substrates are diminished. However, induced curvature rescues the localization, turnover and transferrin cargo uptake activities of CME sites after clathrin, but not AP2, disruption. These data establish that clathrins essential function during CME is to facilitate the evolution of membrane curvature rather than to scaffold CME protein recruitment. SummaryCail et al. demonstrate that induced nanoscale membrane curvature recruits endocytic sites and produces vesicles in cells lacking the coat protein clathrin, while the adaptor protein AP2 is still required, showing that clathrins essential function is to facilitate curvature development of the nascent vesicle.

cell biology↗

bioRxiv2020

Mechanosensing through direct binding of tensed F-actin by LIM domains

Mechanical signals transmitted through the cytoplasmic actin cytoskeleton must be relayed to the nucleus to control gene expression. LIM domains are protein-protein interaction modules found in cytoskeletal proteins and transcriptional regulators; however, it is unclear if there is a direct link between these two functions. Here we identify three LIM protein families (zyxin, paxillin, and FHL) whose members preferentially localize to the actin cytoskeleton in mechanically-stimulated cells through their tandem LIM domains. A minimal actin-myosin reconstitution system reveals that representatives of all three families directly bind F-actin only in the presence of mechanical force. Point mutations at a site conserved in each LIM domain of these proteins selectively disrupt tensed F-actin binding in vitro and cytoskeletal localization in cells, demonstrating a common, avidity-based mechanism. Finally, we find that binding to tensed F-actin in the cytoplasm excludes the cancer-associated transcriptional co-activator FHL2 from the nucleus in stiff microenvironments. This establishes direct force-activated F-actin binding by FHL2 as a mechanosensing mechanism. Our studies suggest that force-dependent sequestration of LIM proteins on the actin cytoskeleton could be a general mechanism for controlling nuclear localization to effect mechanical signaling.

biophysics↗