Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session Y31: Water at Biological InterfacesFocus
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Sponsoring Units: DCP GSOFT Chair: Douglas Tobias Room: 331 |
Friday, March 18, 2016 11:15AM - 11:51AM |
Y31.00001: Characterization of protein hydration by solution NMR spectroscopy Invited Speaker: Joshua Wand A comprehensive understanding of the interactions between protein molecules and hydration water remains elusive. Solution nuclear magnetic resonance (NMR) spectroscopy has been proposed as a means to characterize these interactions but is plagued with artifacts when employed in bulk aqueous solution. Encapsulation of proteins in reverse micelles prepared in short chain alkane solvents can overcome these technical limitations. Application of this approach has revealed that the interaction of water with the surface of protein molecules is quite heterogeneous with some regions of the protein having long-lived interactions while other regions show relatively transient hydration. Results from several proteins will be presented including ubiquitin, staphylococcal nuclease, interleukin 1beta, hen egg white lysozyme (HEWL) and T4 lysozyme. Ubiquitin and interleukin 1beta are signaling proteins and interact with other proteins through formation of dry protein-protein interfaces. Interestingly, the protein surfaces of the free proteins show relatively slowed (restricted) motion at the surface, which is indicative of low residual entropy. Other regions of the protein surface have relatively high mobility water. These results are consistent with the idea that proteins have evolved to maximize the hydrophobic effect in optimization of binding with protein partners. As predicted by simulation and theory, we find that hydration of internal hydrophobic cavities of interleukin 1beta and T4 lysozyme is highly disfavored. In contrast, the hydrophilic polar cavity of HEWL is occupied by water. Initial structural correlations suggest that hydration of alpha helical structure is characterized by relatively mobile water while those of beta strands and loops are more ordered and slowed. These and other results from this set of proteins reveals that the dynamical and structural character of hydration of proteins is heterogeneous and complex. Supported by the National Science Foundation. [Preview Abstract] |
Friday, March 18, 2016 11:51AM - 12:27PM |
Y31.00002: Hydration Dynamics of Biomolecules from Co-solvents to Crowding Invited Speaker: Kevin Kubarych Biomolecules self-assemble into complex functional structures with high fidelity largely due to interactions between the macromolecules and water. Once folded, the dynamics of water molecules in the vicinity of extended macromolecular interfaces can be altered relative to the bulk, leading to complex, heterogeneous and distance-dependent transport properties near these surfaces. Using a strategy based on transition metal carbonyl vibrational probes covalently conjugated to the protein surface, we have been able to use ultrafast two-dimensional infrared (2D-IR) spectroscopy to probe the dynamics from this most important perspective. In a series of studies, we have found these probes to be primarily sensitive to the orientational dynamics of the hydrating water molecules, and have studied both protein/water and membrane/water interfaces. Several key finding have emerged, including a modest 2-3-fold slowdown of hydration water's reorientational dynamics relative to the bulk, and a dynamical transition that occurs due to collective hydration induced by macromolecular crowding. We will summarize our progress to-date, as well as present our newest results on the effects of ions and the dynamical signatures of preferential solvation. [Preview Abstract] |
Friday, March 18, 2016 12:27PM - 12:39PM |
Y31.00003: Observation of Water-Protein Interaction Dynamics with Broadband Two-Dimensional Infrared Spectroscopy Luigi De Marco, Andrew Haky, Andrei Tokmakoff Two-dimensional infrared (2D IR) spectroscopy has proven itself an indispensable tool for studying molecular dynamics and intermolecular interactions on ultrafast timescales. Using a novel source of broadband mid-IR pulses, we have collected 2D IR spectra of protein films at varying levels of hydration. With 2D IR, we can directly observe coupling between water's motions and the protein's. Protein films provide us with the ability to discriminate hydration waters from bulk water and thus give us access to studying water dynamics along the protein backbone, fluctuations in the protein structure, and the interplay between the molecular dynamics of the two. We present two representative protein films: poly-L-proline (PLP) and hen egg-white lysozyme (HEWL). Having no N--H groups, PLP allows us to look at water dynamics without interference from resonant energy transfer between the protein N--H stretch and the water O--H stretch. We conclude that at low hydration levels water-protein interactions dominate, and the water's dynamics are tied to those of the protein. In HEWL films, we take advantage of the robust secondary structure to partially deuterate the film, allowing us to spectrally distinguish the protein core from the exterior. From this, we show that resonant energy transfer to water provides an effective means of dissipating excess energy within the protein, while maintaining the structure. These methods are general and can easily be extended to studying specific protein-water interactions. [Preview Abstract] |
Friday, March 18, 2016 12:39PM - 1:15PM |
Y31.00004: Fluctuating Thermodynamics for Biological Processes Invited Speaker: Sihyun Ham Because biomolecular processes are largely under thermodynamic control, dynamic extension of thermodynamics is necessary to uncover the mechanisms and driving factors of fluctuating processes. The fluctuating thermodynamics technology presented in this talk offers a practical means for the thermodynamic characterization of conformational dynamics in biomolecules. The use of fluctuating thermodynamics has the potential to provide a comprehensive picture of fluctuating phenomena in diverse biological processes. Through the application of fluctuating thermodynamics, we provide a thermodynamic perspective on the misfolding and aggregation of the various proteins associated with human diseases. In this talk, I will present the detailed concepts and applications of the fluctuating thermodynamics technology for elucidating biological processes. [Preview Abstract] |
Friday, March 18, 2016 1:15PM - 1:27PM |
Y31.00005: Thermodynamic properties of water solvating biomolecular surfaces Matthias Heyden Changes in the potential energy and entropy of water molecules hydrating biomolecular interfaces play a significant role for biomolecular solubility and association. Free energy perturbation and thermodynamic integration methods allow calculations of free energy differences between two states from simulations. However, these methods are computationally demanding and do not provide insights into individual thermodynamic contributions, i.e. changes in the solvent energy or entropy. Here, we employ methods to spatially resolve distributions of hydration water thermodynamic properties in the vicinity of biomolecular surfaces. This allows direct insights into thermodynamic signatures of the hydration of hydrophobic and hydrophilic solvent accessible sites of proteins and small molecules and comparisons to ideal model surfaces. We correlate dynamic properties of hydration water molecules, i.e. translational and rotational mobility, to their thermodynamics. The latter can be used as a guide to extract thermodynamic information from experimental measurements of site-resolved water dynamics. Further, we study energy-entropy compensations of water at different hydration sites of biomolecular surfaces. [Preview Abstract] |
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