Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F65: Biomaterials: Structure, Function, Design IIFocus
|
Hide Abstracts |
Sponsoring Units: DBIO Chair: Pupa Gilbert, University of Wisconsin - Madison Room: BCEC 260 |
Tuesday, March 5, 2019 11:15AM - 11:51AM |
F65.00001: Molecular Mechanics of Mussel InspirCopyed Polymers and Coatings Invited Speaker: Phillip Messersmith A number of marine organisms rely on adhesive secretions for attachment to substrates in wet, turbulent environments. In the case of mussels, adhesion is mediated by the byssus- a remarkably strong and tough tissue comprised of collagenous protein threads terminally anchored by an adhesive pad. Byssal proteins have very specialized amino acid compositions, likely related to the specific challenges of achieving adhesion in the wet marine environment. Several byssal proteins contain high levels of 3,4-dihydroxy-L-alanine (DOPA), and there is a growing interest in developing mussel-inspired materials that contain catechols and other functional groups such as primary amine. Mussel inspired coatings derived from the spontaneous polymerization of dopamine, so-called ‘polydopamine’ coatings, have been widely reported in the literature for their ability to be deposited on a variety of substrates. However, the composition of polydopamine remains unknown. In this talk, we will describe our recent results on the molecular mechanics of polydopamine and related coatings using single molecule force spectroscopy. The results favor a ‘polymer’ model of polydopamine structure, casting doubt on models suggesting polydopamine is a supramolecular aggregate of small molecules and oligomers. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F65.00002: Adhesion Strategies of Dictyostelium discoideum - a Force Spectroscopy Study Marco Tarantola, Nadine Kamprad, Hannes Witt, Marcel Schroeder, Christian Titus Kreis, Oliver Baeumchen, Andreas Janshoff Biological adhesion is essential for all motile cells and limits locomotion to |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F65.00003: In-vivo study of Yielding and Post-yielding behavior of Cytoplasm and its linkage with the cytoskeleton Sijie Sun, Jing Xia, David A Weitz We study the yielding and post yielding behavior of cytoplasm in vivo. Cytoplasm, as an omnipresent component of the cells, is known to have finite Young’s modulus and resists deformation, while intracellular cargo transports as fast as micron per second is observed in cytoplasm. In this study, the 3T3 cell line is adapted as a template to investigate the yielding and post yielding behavior of the cytoplasm. We find that cytoplasm yields at 10^2 Pascal scale. The post yielding behavior may be modelled as Bingham fluid. Further control experiment illustrates that both heterogeneity and microtubules significantly contribute to the yielding behavior: The resistance of cytoplasm has multiple resources, and the dynamic assembling and dissembling of the microtubules are essential for yielding. Also, the cytoplasm close to microtubule-organizing centre (MTOC) has higher resistance towards yielding. Our experiment demonstrates the solid to fluid transform of cytoplasm under finite force. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F65.00004: Load-dependent bond kinetics have varied effects on the dynamics and mechanics of actomyosin contractility Pasha Tabatabai, Daniel S. Seara, Ian Linsmeier, Michael Murrell Within the cytoskeleton, myosin motor proteins consume chemical energy and generate mechanical work within the filamentous actin network essential for diverse cell functions like migration, division, and shape change. Myosin unbinding kinetics are force dependent- exhibiting “catch-bond” behavior which decreases the probability of unbinding under load. Altering the binding kinetics of proteins is prohibitively difficult, thus the impact of load dependent binding kinetics on the dynamics and mechanics of actomyosin contractility are unclear. To this end, we use coarse grained molecular dynamics simulations to explore the effect of catch bonds on the accumulation and dissipation of mechanical energy in the actomyosin cytoskeleton. We find that motor binding that increases under load sensitizes the network to myosin motor concentration, increasing the rate of contractility while simultaneously increasing network toughness, or the storage of mechanical energy. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F65.00005: High stretchability, strength and toughness of living cells enabled by hyperelastic vimentin network Jiliang Hu, Yiwei Li, Ming Guo In many normal and abnormal physiological processes, including cellular migration during normal development and invasion in cancer metastasis, cells are required to withstand severe deformations. The structural integrity of eukaryotic cells under small deformations has been known to depend on the cytoskeleton including actin filaments (F-actin), microtubules and intermediate filaments (IFs). However, it remains unclear how cells resist severe deformations since both F-actin and microtubules fluidize or disassemble under moderate strains. Here, we demonstrate that vimentin intermediate filaments (VIFs), a marker of mesenchymal cells, dominate cytoplasmic mechanics at large deformations. Our results show that cytoskeletal VIFs form a stretchable, hyperelastic network. This network works synergistically with other dissipative cytoplasmic components, substantially enhancing the strength, stretchability, resilience and toughness of the living cytoplasm. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F65.00006: Fibril formation kinetics of insulin solutions in an interfacial shearing flow Nicholas Debono, Aditya Raghunandan, Hannah R. Middlestead, A Hirsa The formation of amyloid fibril plaques and the accumulation of such structures in vivo is the hallmark of disorders such as Alzheimer’s and type-II diabetes. Fibril formation can be accelerated by several factors including changes to pH and temperature conditions. However, the role of the dominant and most varying in vivo factors of fluid flow and shear at hydrophobic interfaces in protein aggregation pathways remain poorly understood. Proteins adsorbed at the air/fluid interface are also subjected to significant hydrodynamic stresses during bioprocessing and drug handling, which leads to unwarranted denaturation/aggregation and subsequent loss in drug efficacy. Here, we study the kinetics of fibril formation for human recombinant insulin solutions in an interfacial shearing flow using fixed time-point ThT fluorescence and native-protein absorbance assays across a wide range of rotation rates. We identify differences in the morphology of the fibril structures formed at the air/fluid interface and in bulk solution at different stages of fibril seeding and growth. This is key to elucidating the aggregation pathway and toxicity of shear-induced denaturation and protein fibril formation. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F65.00007: MULTI-SCALE MICRORHEOLOGY USING FLUCTUATING SEMIFLEXIBLE FILAMENTS AS STEALTH PROBES Kengo Nishi, Christoph F. Schmidt, Frederick MacKintosh Microrheology is commonly performed using micron-sized beads embedded in the (soft) medium to be studied. Inserting beads can be problematic in confined or hard to access places and can cause artifacts. Here, we introduce the use of single-walled carbon nanotubes (SWNTs), which are model semi-flexible polymers with non-photobleaching fluorescence, as “stealth probes”. We embedded SWNTs in viscoelastic media and analyzed thermally driven shape fluctuations. We show that the bending dynamics of SWNTs embedded in soft media can be used to probe the viscoelastic properties of such media at multiple scales, corresponding to the wavelengths of the modes analyzed. We found that the viscoelastic moduli of polymer solutions measured by SWNTs are in excellent agreement with those by measured by conventional micro/macrorheology, which validates the method. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F65.00008: In situ imaging of strained collagen fibrils Chris Peacock, Laurent Kreplak Damage to collagenous tissues remain difficult to treat due to uncertainty of how their constituents operate under tension. The smallest of these constituents is the collagen fibril, a rope-like aggregate of collagen molecules with a structure comparable to man-made fibres. While the force-elongation curve of collagen fibrils is fairly well characterized, structural changes due to elongation remain poorly understood. In this talk I will present an in situ atomic force microscopy approach to probe the morphology and cohesiveness of strained fibrils. |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F65.00009: Collagen-inspired self-assembly of twisted filaments Martin Falk, Lucy Colwell, Amy Duwel, Michael Phillip Brenner There have been dramatic developments in our ability to functionalize submicron scale objects with molecules enabling specific interactions between building blocks, opening up an enormous design space for solutions of particular engineering problems. Here, we explore the physics of collagen self-assembly in order to deduce design rules for the self-assembly of twisted filaments. Despite the well-known structure of collagen, identifying which aspects of its design are required for reproducing collagen-like features in synthetic analogues is unknown. Using computer simulations, we propose a scheme mediated by specific interactions to self-assemble collagen-like triple helices. The assembly nucleates chiral defects, in which two of the filaments switch orientations. Such defects can be eliminated with a modest energetic bias, or nucleated by introducing mechanical weak spots. By inducing spatial variation of the enthalpy of helix formation, we can localize another type of defect where the helix becomes locally unbound. Local unbinding slows assembly, evoking kinetic pathologies previously ascribed to mutations in the primary collagen amino acid sequence. In analogy to collagen, controlled formation of defects could enable hierarchical self-assembly of bundles of twisted filaments. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F65.00010: Mechanism of metal-like conductivity in bacterial protein nanowires Sophia Yi, Yangqi Gu, Jens Neu, J. Patrick O'brien, Sibel Ebru Yalcin, Dennis Vu, Winston Huynh, Victor Batista, Charles A Schmuttenmaer, Nikhil Malvankar Proteins are considered electronically insulators. However, nanofilaments produced by Geobacter sulfurreducens exhibit metal-like conductivity. To elucidate the mechanism of electron transport, we measured the electrical and optical conductivity of filaments from multiple mutant strains as a function of molecular length, temperature, frequency, pH and π-stacking. We demonstrate that intrinsic conductivity of individual filaments can be described by theoretical model for quasi-one-dimensional materials. To determine the molecular architecture responsible for conductivity, we are using a suite of complementary experimental and computational methods. Our studies show that filaments show π-stacking, that can cause intermolecular electron delocalization, conferring metallic conductivity to filaments. Furthermore, increasing π-stacking improves their crystallinity, yielding a longer mean free path for electrons, and stronger electronic coupling which yields 1000 times lower electron attenuation than other proteins. These studies will help development of genetically programmable biomolecular materials with tunable functionality through precise control of their electronic and protein structure. |
Tuesday, March 5, 2019 1:39PM - 2:15PM |
F65.00011: Cancer, p53, and non-classical self-assembly of amyloids and their first order phase transitions Invited Speaker: Peter Vekilov About half of human cancers are associated with mutations of the tumor suppressor p53. Gained oncogenic functions of the mutants have been related to aggregation behaviors of wild-type and mutant p53. The thermodynamic and kinetic mechanisms of p53 aggregation are poorly understood. Here we find that wild-type p53 forms an anomalous liquid phase. The liquid condensates exhibit several behaviors beyond the scope of classical phase transition theories: their size, ca. 100 nm, is independent of the p53 concentration and decoupled from the protein mass held in the liquid phase. Thermodynamic analyses elucidate another unusual property of this liquid phase: lack of constant solubility. The nucleation of p53 fibrils deviates from the accepted mechanism of sequential association of single solute molecules. We find the liquid condensates serve as pre-assembled precursors of high p53 concentration that facilitate fibril assembly. Fibril nucleation hosted by precursors represents a novel biological pathway, which opens avenues to suppress protein fibrillation in aggregation diseases. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700