THE OPTIMIZATION OF PROTEIN-SOLVENT INTERACTIONS - THERMOSTABILITY AND THE ROLE OF HYDROPHOBIC AND ELECTROSTATIC INTERACTIONS

Protein-solvent interactions were analyzed using an optimization param eter based on the ratio of the solvent-accessible area in the native a nd the unfolded protein structure. The calculations were performed for a set of 183 nonhomologous proteins with known three-dimensional stru cture available in the Protein Data Bank. The dependence of the total solvent-accessible surface area on the protein molecular mass was anal yzed. It was shown that there is no difference between the monomeric a nd oligomeric proteins with respect to the solvent-accessible area. Th e results also suggested that for proteins with molecular mass above s ome critical mass, which is about 28 kDa, a formation of domain struct ure or subunit aggregation into oligomers is preferred rather than a f urther enlargement of a single domain structure. An analysis of the op timization of both protein-solvent and charge-charge interactions was performed for 14 proteins from thermophilic organisms. The comparison of the optimization parameters calculated for proteins from thermophil es and mesophiles showed that the former are generally characterized b y a high degree of optimization of the hydrophobic interactions or, in cases where the optimization of the hydrophobic interactions is not s ufficiently high, by highly optimized charge-charge interactions.