Hydrophilic residues at the apical domain of GroEL contribute to GroES finding but attenuate polypeptide binding

The GroES binding site at the apical domain of GroEL, mostly consisting of hydrophobic residues, overlaps largely with the substrate poly-peptide bind ing site. Essential contribution of hydrophobic interaction to the binding of both GroES and polypeptide was exemplified by the mutant GroEL(L237Q) wh ich lost the ability to bind either of them. The binding site, however, con tains three hydrophilic residues, E238, T261, and N265. For GroES binding N 265 is essential since GroEL(N265A) is unable to bind GroES. E238 contribut es to rapid GroES binding to GroEL because GroEL(E238A) is extremely sluggi sh in GroES binding. Polypeptide binding was not impaired by any mutations of E238A, T261A, and N365A. Rather, these mutants, especially GroEL(N265A), showed stronger polypeptide binding affinity than wild-type GroEL. Thus, t hese hydrophilic residues have a dual role; they help GroES binding on one hand but attenuate polypeptide binding on the other hand. (C) 2000 Academic Press.