Heteroenergetics of Bovine Serum Albumin Adsorption from Good Solvents Related to Crystallization Conditions

Total internal reflection fluorescence (TIRF) was applied to study adsorption of bovine serum albumin (BSA) from a thermodynamically good solvent commonly used as a buffer for BSA crystallization. BSA adsorption is shown to exhibit heteroenergetics, which is possibly a general property of protein interfacial behavior. For example, BSA adsorption on quartz, SnO2 , and alkyl-modified surfaces demonstrates broad continuous distributions of energies of adsorption activation and protein-surface binding. For heteroenergetic adsorption, the type of the isotherm and kinetics depends on the type of the energy distribution functions and the type of correlation between the energies. In the case of BSA adsorption on quartz and SnO2 surfaces, protein interfacial behavior is consistent with a model suggesting rectangular distributions both of activation energies of adsorption and energies of protein-surface binding. In the case of an alkyl-modified surface, BSA adsorption kinetics is interpreted in terms of a heteroenergetic model suggesting initial adsorption at selected adsorption sites with maximum rate constants. The model also suggests that lateral diffusion quickly redistributes the molecules from the initial adsorption sites to the sites with higher binding energies. The combination of TIRF spectroscopy with an electrochemical system was used to study the effect of surface charge on protein adsorption on a transparent SnO2 electrode. BSA behavior on the SnO2 electrode was found to correlate with surface hydrophobicity and indifferent to charges both of the surface and the protein. Hydrophobic interactions seem to be the principal driving force in determining the behavior of BSA at the solid-liquid interface and likely plays an important role in protein crystallogenesis.