Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R48: Physics of Intracellular Membranes and OrganellesFocus Session
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Sponsoring Units: GSNP DBIO Chair: Bodo Wilts, University of Fribourg Room: LACC 510 |
Thursday, March 8, 2018 8:00AM - 8:36AM |
R48.00001: Abstract Withdrawn Invited Speaker:
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Thursday, March 8, 2018 8:36AM - 8:48AM |
R48.00002: Formation of Coatless Membrane Vesicles Susanne Liese, Rossana Rojas, Eva Wenzel, Camilla Raiborg, Harald Stenmark, Andreas Carlson
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Thursday, March 8, 2018 8:48AM - 9:00AM |
R48.00003: Impedance Spectroscopy as a Label-free Probe of Mitochondrial Membrane Potential Pavithi Weerasinghe, Jarek Wosik, Wanda Zagozdzon-Wosik, Uday Karlapudi, Dale Hamilton, Aijun Zhang, Martha Villagran, John Miller The mitochondrial membrane potential drives the synthesis of adenosine triphosphate (ATP) - the chemical currency of energy for all living organisms. Recent studies suggest that the low-frequency dielectric response, extracted from impedance of a suspension of mitochondria, correlates with their average membrane potential. Energetic electrons donated by molecules extracted from food, build up the proton gradient and membrane potential that drives ATP production. These electrons ultimately recombine with protons and oxygen to form water. Changes in mitochondrial oxygen consumption are therefore expected to correlate with changes in membrane potential and with impedance. We fabricated an impedance probe designed to enable impedance and oxygen consumption rate measurements simultaneously within a respirometer. Further tests include addition of substrates known to affect oxygen consumption, such as ADP, FCCP and succinate. These are used to correlate changes in respiration rate with impedance and, ultimately, mitochondrial membrane potential. Novel substrates, such as excess dopamine, can finally be assessed for possible adverse effects. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R48.00004: Localization of thermal fluctuations on membranes with complex geometry Alexander Levine The geometry of elastic membranes in their stress-free state affects both their mechanics and the spatial distribution of their thermal fluctuations. This effect results from the fact that membrane curvature introduces a geometric coupling between the soft out-of-plane bending modes and stiffer, in-plane elastic deformation. As a result, curved membranes have complex distributions of thermal fluctuations in equilibrium. Using shallow shell theory combined with equilibrium statistical physics, we demonstrate that thermalized membranes containing regions of negative Gaussian curvature develop anomalously large fluctuations. Moreover, the existence of special curves, “singular lines,” leads to a breakdown of linear membrane mechanics. These singular lines effectively partition the membrane into regions whose fluctuations are only weakly coupled. We test these predictions using high-resolution microscopy of human red blood cells as a case study. Our observations show geometry-dependent localization of thermal fluctuations demonstrating the important role of geometry in membrane mechanics and fluctuations. |
(Author Not Attending)
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R48.00005: Active Intracellular Trafficking Dynamics Drives Membrane Morphologies Alex Rautu, Kripa Gowrishankar, Richard Morris, Madan Rao We study the role of the membrane recycling on the morphology of closed membranes, such as those encountered on organelles within the eukaryotic cell. These constantly exchange membrane material amongst themselves, encapsulated in small transport vesicles, along highly regulated trafficking pathways. The process of fusion and fission is performed by a complex interacting biochemical network of proteins, requiring chemical energy via the hydrolysis of ATP or GTP. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R48.00006: Modeling multicomponent phase behavior inspired by membraneless compartmentalization in cells Sheng Mao, Mikko Haataja, Andrej Kosmrlj Recent evidence shows that intracellular phase separation can drive the formation of membraneless liquid-like droplets composed of protein RNA and other biomolecules. Gibbs rule suggests that the number of possible coexisting phases scales linearly with the number of components, which is on the order of hundreds in cells. However, in typical biological systems only a small number of phases are observed and they are often assembled in highly organized structures. To resolve this puzzle, we first employ Flory-Huggins theory to examine the global phase structure of many components, whose interaction energies are randomly drawn from a Gaussian distribution. We find that the typical number of coexisting phases is primarily determined by the composition and the mean strength of interaction. However, the enhanced variance of interaction increases the range of parameters, where small number of coexisting phases are observed. In order to see, how different phases evolve in time and arrange in space, we used the Cahn-Hilliard formalism. We investigate the nucleation and growth of domains as well as their relative packing for 3, 4, 5 and more components. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R48.00007: Butterfly gyroid nanostructures as a time-frozen glimpse of intracellular membrane development Gerd Schroeder-Turk, Benjamin Apeleo Zubiri, Michael Klatt, Benjamin Butz, Michael Fischer, Stephen Kelly, Erdmann Spiecker, Ullrich Steiner, Bodo Wilts The formation of the biophotonic gyroid material in butterfly wing scales is an exceptional feat of evolutionary engineering of functional nanostructures. It is hypothesized that this nanostructure forms by chitin polymerization inside a convoluted membrane of corresponding shape in the endoplasmic reticulum. However, this dynamic formation process, including whether membrane folding and chitin expression are simultaneous or sequential processes, cannot yet be elucidated by in vivo imaging. We report an unusual hierarchical ultrastructure in the butterfly Thecla opisena that, as a solid material, allows high-resolution three-dimensional microscopy. Rather than the conventional polycrystalline spacefilling arrangement, a gyroid occurs in isolated facetted crystallites with a pronounced size gradient.When interpreted as a sequence of time-frozen snapshots of the morphogenesis, this arrangement provides insight into the formation mechanisms of the nanoporous gyroid material as well as of the intracellular organelle membrane that acts as the template. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R48.00008: Sidedness and Heigh-Offset Effects on the 2D Self-Assembly of the Hexagonal Tiles of Bacterial Microcompartments Nic Ezzell, Peter Doak, Artem Maksov, Maxim Ziatdinov, Miguel Fuentes-Cabrera, J.P. Mahalik Bacterial micro-compartments, BMCs, are organelles that exists in a variety of bacteria. They are composed of an outer-shell, comprised of hexagonal and pentagonal proteinaceous tiles, that encapsulates enzymes that perform many different types of reactions. Because of the variety of tiles that exists, and the possibility of combining them for producing molecular scaffolds with tailored permeability and enzymatic properties, understanding the self-assembly of BMCs is receiving considerable attention. We recently investigated the initial stages of 2D self-assembly of hexagonal tiles using an approach that combined atomistic and coarse-grained force-fields. Here, we present a new approach, where the coarse-grained force-field is mapped onto a look-up table. With it, we have investigated the self-assembly of islands containing hundreds of hexagonal tiles, and found that it depends not only on the sidedness of the tiles but also on their relative height. Our work also puts forward a user-friendly computational interface that we hope will aid experimentalists interested in knowing, beforehand, what kind of structures will result from combining a particular set of tiles. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R48.00009: Mechanisms of organelle biogenesis govern stochastic fluctuations in organelle copy number Shankar Mukherji Among the defining properties of the eukaryotic cell is its organization into spatial compartments known as organelles, specialized biochemical environments crucial for processes fundamental to life. Coordinating organelle copy number, size, and composition with developmental and environmental cues is one of the chief ways the cell can match its biochemical capabilities with its physiological demands. How precisely does the cell orchestrate flows of matter and energy to produce exquisitely defined organelles at the nanometer and femtoliter scales of a cell? Using a stochastic model of organelle copy number control, we show that cell-to-cell fluctuations in budding yeast organelle copy numbers can be used to infer the mechanisms by which organelle copy numbers are regulated. We show how our fluctuation-based inferences suggest resolutions to controversies surrounding the biogenesis of peroxisomes and lipid droplets, organelles responsible for major steps in lipid metabolism. By studying correlations in fluctuations of distinct organelles, we hope to infer the decision-making principles cells utilize to remodel their organelle makeup to respond to external signals. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R48.00010: In vivo phase and dynamical behavior of intracellular lipid droplets Margarita Fomina, Eugene Mamontov, Hugh O'Neill Lipid Droplets are complex cellular organelles generated by all cells in response to elevated fatty acid levels. They represent a core full of triacylglycerols enclosed by a phospholipid monolayer with embedded associated proteins. LD is a source of lipids for metabolism and membrane synthesis. However, knowledge of the state and internal molecular motions of LD in its natural environment, whole cell, is lacking. |
Thursday, March 8, 2018 10:24AM - 11:00AM |
R48.00011: The Cellular and Genetic Basis for Structural Color in Butterflies Invited Speaker: Nipam Patel Research into the optical properties of structurally colored butterfly scales has been remarkably successful and revealed a great deal about the physical basis of color production in a myriad of species. Most of the studies are focused on adult scales, and often driven by the desire to eventually engineer these color-producing nanostructures using non-biological approaches. Our emphasis has been to understand how biological systems, in this case individual scale cells, are able to produce specific structures, particularly how these cells are able to pattern intracellular membranes and other cellular component to create the templates for the nanostructures. We have focused primarily on two systems. |
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