Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session J1: Experiments in Biophysics |
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Chair: Alberto Perez, Laufer Center for Physical and Quantitative Biology Room: 235, Campus Center, NJIT |
Saturday, November 4, 2017 4:15PM - 4:51PM |
J1.00001: Entropy in Protein Function Invited Speaker: Joshua Wand Biological processes are most often controlled using molecular recognition by proteins. The physical origin of high affinity interactions involving proteins continues to be the subject of intense investigation. Conformational entropy represents perhaps the last piece of the thermodynamic puzzle that governs protein structure, stability, dynamics and function. The importance of internal conformational entropy in proteins has been debated for decades but has resisted experimental quantification. Recently we have developed and validated an NMR-based approach that uses a dynamical proxy to determine changes in conformational entropy. This approach, which we term the ``entropy meter,'' requires few assumptions, is empirically calibrated, and is apparently robust and universal. It can now be shown that proteins retain considerable conformational entropy in their native functional states and that this entropy can play a decisive role in the thermodynamics of molecular recognition. Changes conformational entropy of a protein upon binding a high affinity ligand are system specific and can vary from strongly inhibiting to even strongly promoting binding. Thus one cannot understand how proteins work without considering conformational entropy. This approach also allows for the refinement of empirical coefficients that relate changes in accessible surface area to changes in the entropy of water and the determination of the loss of rotational-translational entropy in high affinity protein complexes. [Preview Abstract] |
Saturday, November 4, 2017 4:51PM - 5:27PM |
J1.00002: Correlative cryo-fluorescent and electron microscopy for biological applications. Invited Speaker: Gleb Shtengel Chemical fixation is a standard procedure used in preparation for optical microscopy of biological samples. Unfortunately, chemical fixation produces various artefacts and may destroy cellular ultrastructure. Cryo-fixation offers an alternative way of preserving a sample in a life-like state. While cryo-fixation poses challenges for subsequent imaging, it also allows for different imaging modalities. The photo-physical properties of fluorescent labels can be very different at low temperature, so the combination of fluorescent labels and light imaging methodology needs to be reevaluated.~ Furthermore, good ultrastructure preservation allows for subsequent high-quality electron microscopy imaging, thus permitting correlated optical and electron microscopy imaging. We will describe the instruments and methods we developed for preparation and imaging of cultured cells using cryo-fluorescent and electron microscopy. [Preview Abstract] |
Saturday, November 4, 2017 5:27PM - 5:39PM |
J1.00003: Quantifying Heterogeneous Aggregation of Polymer Particles in Blood Plasma Kathleen McEnnis, Joerg Lahann Polymer particles are often studied as drug delivery vehicles, but little is known about their behavior in blood once injected into animal models. If the particles aggregate in blood, they will be removed from circulation instead of reaching the intended target. Typically dynamic light scattering (DLS) is used to analyze aggregation behavior, but DLS cannot be used in blood because the components of blood also scatter light. In this work, an alternative method of analyzing particles in blood plasma has been developed using nanoparticle tracking analysis (NTA) with fluorescent filters. NTA was used to analyze the aggregation behavior of fluorescent polystyrene particles (200 nm in diameter) in blood plasma. Particles were tested with polyethylene glycol (PEG) ligands and without any surface modification. A large number of heterogeneous aggregates of particles with components of the blood plasma were observed and quantified. The addition of PEG ligands was found to decrease the percentage of particles forming aggregates. The use of this characterization method will allow for better understanding of particle behavior in the body, and potential problems, specifically aggregation, can be addressed before investing in in vivo studies. [Preview Abstract] |
Saturday, November 4, 2017 5:39PM - 6:15PM |
J1.00004: Using flow to measure membrane properties Invited Speaker: Aurelia Honerkamp-Smith While most life takes place in an aqueous environment, the physics of micro-scale movement in fluid environments can be counterintuitive. I will discuss recent experiments with the theme of building up a three-dimensional, microscopic picture of motion. Multi-component lipid membranes act like two-dimensional fluids, whose flow can be observed to couple closely to that of the surrounding water. This fluidity can be used to ask questions about the physical properties of lipids and membrane proteins. [Preview Abstract] |
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