EXTENT AND NATURE OF CONTACTS BETWEEN PROTEIN MOLECULES IN CRYSTAL LATTICES AND BETWEEN SUBUNITS OF PROTEIN OLIGOMERS

A survey was compiled of several characteristics of the intersubunit c ontacts in 58 oligomeric proteins, and of the intermolecular contacts in the lattice for 223 protein crystal structures, The total number of atoms in contact and the secondary structure elements involved are si milar in the two types of interfaces, Crystal contact patches are freq uently smaller than patches involved in oligomer interfaces, Crystal c ontacts result from more numerous interactions by polar residues, comp ared with a tendency toward nonpolar amino acids at oligomer interface s. Arginine is the only amino acid prominent in both types of interfac es, Potentials of mean Terce far residue-residue contacts at both crys tal and oligomer interfaces were derived from comparison of the number of observed residue-residue interactions with the number expected by mass action, They show that hydrophobic interactions at oligomer inter faces favor aromatic amino acids and methionine over aliphatic amino a cids; and that crystal contacts form in such a way as to avoid inclusi on of hydrophobic interactions, They also suggest that complex salt br idges with certain amino acid compositions might be important in oligo mer formation, For a protein that is recalcitrant to crystallization, substitution of lysine residues with arginine or glutamine is a recomm ended strategy. (C) 1997 Wiley-Liss, Inc.