Modelling molecular stability in gamma B crystallin

Molecular modelling and dynamics simulations of gamma B crystallin and a number of its adducts were used to simulate effects of post-translational modifications. N-terminal modifications which disrupted the surface charge network of gamma-crystallin did not produce significant unfolding in any part of the gamma-crystallin molecule (P > 0.05) consistent with the results of in vitro aggregation studies. There were no significant changes to the molecular volume of the protein, suggesting that adduct formation did not result in molten globule formation. Adduct formation did however increase the vulnerability of particular gamma-crystallin cysteine residues to sulphydryl bond formation and so increased the possibility of mixed disulphide formation with glutathione. Modelling of such secondary modification products (containing both N-terminal modifications and glutathione adducts) demonstrated significant (P < 0.05) structural changes. This suggests that a post-translational modification pathway leading to crystallin cross-linking and cataractogenesis proceeds via a number of co-operative steps involving both modification at the N-terminus and mixed glutathione formation.