VAN-DER-WAALS INTERACTIONS INVOLVING PROTEINS

Van der Waals (dispersion) forces contribute to interactions of protei ns with other molecules or with surfaces, but because of the structura l complexity of protein molecules, the magnitude of these effects is u sually estimated based on idealized models of the molecular geometry, e.g., spheres or spheroids. The calculations reported here seek to acc ount for both the geometric irregularity of protein molecules and the material properties of the interacting media. Whereas the latter are f ound to fall in the generally accepted range, the molecular shape is s hown to cause the magnitudes of the interactions to differ significant ly from those calculated using idealized models, with important conseq uences. First, the roughness of the molecular surface leads to much lo wer average interaction energies for both protein-protein and protein- surface cases relative to calculations in which the protein molecule i s approximated as a sphere. These results indicate that a form of ster ic stabilization may be an important effect in protein solutions. Unde rlying this behavior is appreciable orientational dependence, one refl ection of which is that molecules of complementary shape are found to exhibit very strong attractive dispersion interactions. Although this has been widely discussed previously in the context of molecular recog nition processes, the broader implications of these phenomena may also be important at larger molecular separations, e.g., in the dynamics o f aggregation, precipitation, and crystal growth.