NMR study of the cataract-linked P23T mutant of human γD-crystallin shows minor changes in hydrophobic patches that reflect its retrograde solubility

Abstract

The Pro23 to Thr (P23T) mutation in human γD-crystallin (HGD) shows several cataract phenotypes. We found earlier [A. Pande, O. Annunziata, N. Asherie, O. Ogun, G.B. Benedek, J. Pande, Decrease in protein solubility and cataract formation caused by the Pro23 to Thr mutation in human gamma D-crystallin, Biochemistry 44 (2005) 2491–2500] that the mutation dramatically lowers the solubility of P23T but the overall protein fold is maintained. Recently we observed that solutions of P23T showed liquid–liquid phase transition behavior similar to that of HGD but the liquid–protein crystal phase transition was altered, suggesting an asymmetric distribution of “sticky” patches on the protein surface [J.J. McManus, A. Lomakin, O. Ogun, A. Pande, M. Basan, J. Pande, G.B. Benedek, Altered phase diagram due to a single point mutation in human gammaD-crystallin, Proc. Natl. Acad. Sci. USA 104 (2007) 16856–16861]. Here we present high-resolution NMR studies of HGD and P23T in which we have made nearly complete backbone assignments. The data provide a structural basis for explaining the retrograde solubility of P23T by (a) identifying possible “sticky” patches on the surface of P23T and (b) highlighting their asymmetric distribution.