Bulletin of the American Physical Society
Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020; Virtual
Session C01: Physics of Biological Membranes |
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Chair: Normand Mousseau, Universite de Montreal |
Friday, December 4, 2020 4:30PM - 5:06PM |
C01.00001: Fundamental physics of flow-mediated membrane protein transport. Invited Speaker: Aurelia Honerkamp-Smith A remarkable feature of lipid membranes is their fluidity, which allows them to self-heal, bend, and flow. Membranes circulate in response to flows in the water surrounding them, but cell membranes are reinforced by a cytoskeletal network of protein filaments which modifies their fluid properties, making their behavior complex and challenging to predict. Cell flow responses regulate diverse processes such as blood pressure, bone density, and neural growth. However, we lack information on the lateral movement of extracellular membrane proteins located at the cell-fluid interface. We use model membranes, microfluidics and microscopy to investigate how fundamental properties of supported membranes change when flow is applied to them. [Preview Abstract] |
Friday, December 4, 2020 5:06PM - 5:18PM |
C01.00002: Modeling Nucleation and Kinetics of Clathrin Assembly by Membrane Localization Sikao Guo, Margaret Johnson The formation of clathrin lattices on the plasma membrane of cells is a multi-component assembly process which plays an essential role in transport across the membrane. Here we develop a microscopic model that can quantitatively reproduce recent in vitro fluorescence experiments, establishing how cooperativity due to both 2D membrane localization and adaptor protein interactions are necessary to drive the nucleation and growth of clathrin cages. This model is also consistent with the known biochemistry of protein interactions. We simulated this model using the structure-resolved reaction-diffusion simulator NERDSS, collecting minutes-long movies of the clathrin assembly on the membrane. We then show how changing the stickiness of the membrane controls the nucleation of clathrin-coated structures on the surface, with clathrin present now at physiologic concentrations. With this model, we can predict how tuning the stoichiometry of components will impact the nucleation and stability of clathrin cages on membranes, resulting in productive or abortive assembly events. This model and corresponding simulations provide a critical quantitative framework for investigating how the selection of cargo at membranes by associated adaptors controls the speed and success of vesicle formation. [Preview Abstract] |
Friday, December 4, 2020 5:18PM - 5:54PM |
C01.00003: A Multiscale Study on the Mechanisms of Spatial Organization in Ligand-receptor Interactions on Cell Surfaces. Invited Speaker: zhaoqian su The binding of cell surface receptors with extracellular ligands triggers distinctive signaling pathways, leading into the corresponding phenotypic variation of cells. After ligands and receptors form complexes through trans-interactions, they can further oligomerize into higher-order structures with additional cis-interactions. This ligand-receptor oligomerization on cell surfaces plays a functional role in regulating cell signaling. The underlying mechanism, however, is not well understood. One typical example is proteins that belong to the tumor necrosis factor receptor (TNFR) superfamily. Using a new multiscale simulation platform that spans from atomic to subcellular levels, we compared the detailed physical process of ligand-receptor oligomerization for two specific members in the TNFR superfamily. Interestingly, although these two systems share high similarity on the tertiary and quaternary structural levels, our results indicate that their oligomers are formed with very different dynamic properties and spatial patterns. We demonstrated that the changes of receptor's conformational fluctuations due to the membrane confinements are closely related to such difference. This study, therefore, provides the molecular basis to TNFR oligomerization and reveals new insights to TNFR-mediated signal transduction. Moreover, our multiscale simulation framework serves as a prototype that paves the way to study higher-order assembly of cell surface receptors in many other bio-systems. [Preview Abstract] |
Friday, December 4, 2020 5:54PM - 6:06PM |
C01.00004: Coronavirus Envelope Protein: Lipid Sensitivity and Membrane Bending Jesse Sandberg, Grace Brannigan The Coronavirus envelope (E) protein is a pentameric viroporin that is implicated in numerous viral processes including but not limited to assembly, budding, envelope formation, and pathogenesis. While much work has recently been done to characterize this protein's structure, function, and interactions with other proteins, its interactions with and effects on surrounding membranes are less well understood. It is known that the viroporin loses ion-selectivity in an exclusively neutral lipid environment, but it is not clear what drives this behavior. In the present study we use coarse-grain molecular dynamics (CG-MD) simulations to identify stable binding sites for anionic lipid headgroups. We then use all-atomistic molecular dynamics simulations to investigate the effect of lipid charge on viroporin structure using the sites identified from CG-MD. The E protein also induces membrane curvature, although the precise mechanism is unknown. Using CG-MD, we observe that the E protein bends the membrane in simulations with lipid species that have long acyl chains. We find this effect is limited when shorter lipid species are used, which suggests it results from asymmetric mismatch between the viroporin transmembrane domain and the thickness of a typical host membrane. [Preview Abstract] |
Friday, December 4, 2020 6:06PM - 6:18PM |
C01.00005: Protein binding to a curved and enclosed membrane with the continuum membrane model. YIBEN FU, Jeanne Stachowiak, Margaret Johnson Localization of proteins to a membrane surface is an essential step in a broad range of biological processes such as clathrin-mediated endocytosis. Some proteins exhibit abilities of the curvature induction and curvature sensing. The sensing of membranes with varying curvature by inserting amphipathic helices has been characterized using both experiments and models based on elasticity theory. Here, we show that the recruitment of each domain to the membrane can influence subsequent binding events, effectively changing the `stickiness' of the membrane. We consider the ability of both weak protein-protein interactions, and mechanical feedback of the membrane, in driving these changes in membrane stickiness. Here we use a thin-film continuum membrane model to quantify how protein insertions alter the energetics of small unilamellar vesicles of varying sizes. Our model reproduces previous experimental results showing that the energetics of interactions are stronger to smaller vesicles. We are then able to quantify how multiple insertions can produce cooperativity in the energy. Our results provide a mechanism through which recruitment of proteins to membranes can create positive feedback, increasing the probability of subsequent binding events. And this positive feedback is due to membrane mechanics rather than protein-protein interactions. Quantifying these mechanisms is critical for understanding the dynamics and control of proteins that remodel membranes through localization and self-assembly in a range of cellular processes. [Preview Abstract] |
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