The cataract-causing mutation G75V promotes γS-crystallin aggregation by modifying and destabilizing the native structure

Congenital cataract is one of the leading causes of childhood blindness worldwide. About half of heredity cataracts are caused by mutations in various crystallins. However, the underlying mechanisms have not been elucidated for most of crystallin mutations. In this research, we studied the effect of a cataract-causing mutation G75V on γS-crystallin structure, stability and aggregatory propensity. Spectroscopic experiments indicated that the mutation had little impact on γS-crystallin oligomeric status and secondary structure components, but led to large perturbations in tertiary structure. Compared with the WT protein, the G75V mutant had more solvent-accessible Trp fluorophores and hydrophobic exposure. The modified native state of mutant γS-crystallin was more susceptible to environmental stresses such as heat treatment, guanidine hydrochloride and acid conditions. The destabilized mutated protein was more prone to form large aggregates when denatured by high temperature or UV-irradiation. The thermal aggregation of the G75V mutant could be successfully inhibited by excess amount of αA-crystallin with a higher efficiency than the WT protein. Our results suggested that the aberrant modifications in γS-crystallin structure might contribute to the lower stability and higher aggregatory potency of the mutated protein, which subsequently resulted in cataracts in the patients.