Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Wednesday Speaker Abstracts

Effects of Molecular Crowding and Reversible Adsorption on Macromolecular Self- assembly: a Mesoscopic Analysis Allen Minton . NIDDK-NIH, Bethesda , USA. Previously published simplified statistical-thermodynamic models for the effect of volume exclusion (‘crowding’) and for the effect of surface adsorption upon the self-association of a dilute tracer protein are reviewed. A recently developed model for the cumulative effect of both crowding and adsorption on protein fibrillation is presented. This model predicts that when the volume fraction of "inert" crowder exceeds a critical value, or the enthalpy of tracer adsorption becomes more negative than a critical value, the slightly fibrillated and highly soluble tracer protein will condense onto the surface and simultaneously achieve a very high degree of fibrillation. Aqueous Amino Acids and Proteins Near Solid Surfaces and Air-Water Interfaces Marek Cieplak . Polish Academy of Sciences, Warsaw, Poland. A systematic comparison of the adsorptive properties of various surfaces can be accomplished by considering a set of reference biomolecules. We have initiated such a program by selecting the twenty natural amino acids, some dipeptides, and a small protein - tryptophan cage as the reference systems for all-atom simulational studies. The surfaces compared are: ZnS, gold, cellulose Iβ, mica, and four faces of ZnO. The specificities, as determined through the potential of the mean force for the amino acids, are found to depend on the solid, its face and, for gold, on the choice of the force field (hydrophobic, hydrophilic, or incorporating the polarizability of the metal). We demonstrate that binding energies of dipeptides and tripeptides are smaller than the combined binding energies of their amino acidic components. The water density and polarization profiles are also surface-specific. The first water layer that forms near the strongly hydrophilic ZnO corresponds to packing at such a density that even single residues cannot reach the solid. ZnS is more hydrophobic and yields only minor articulation of water into layers. In the case of ZnS, not all amino acids can attach to the surface and when they do, the binding energies are comparable to those found for the surfaces of ZnO (and to hydrogen bonds in proteins). For the hydrophobic Au, adsorption events of tryptophan cage are driven by attraction to the strongest binding amino acids. This is not so for ZnO, ZnS and for the hydrophilic models of gold. Studies of several proteins near mica, with a net charge on its surface, indicate existence of two types of states: deformed and unfolded. Using a coarse-grained model, we also study the glassy behavior of protein layers at air-water interfaces.

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