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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.