Cataract-Causing S93R Mutant Destabilized Structural Conformation of βB1 Crystallin Linking With Aggregates Formation and Cellular Viability

Cataract, opacity of the eye lens, is the leading cause of visual impairment worldwide. The crucial pathogenic factors that cause cataract are misfolding and aggregation of crystallin protein. beta B1-crystallin, which is the most abundant water-soluble protein in mammalian lens, is essential for lens transparency. A previous study identified the missense mutation beta B1-S93R being responsible for congenital cataract. However, the exact pathogenic mechanism causing cataract remains unclear. The S93 residue, which is located at the first Greek-key motif of beta B1-crystallin, is highly conserved, and its substitution to Arginine severely impaired hydrogen bonds and structural conformation, which were evaluated via Molecular Dynamic Simulation. The beta B1-S93R was also found to be prone to aggregation in both human cell lines and Escherichia coli. Then, we isolated the beta B1-S93R variant from inclusion bodies by protein renaturation. The beta B1-S93R mutation exposed more hydrophobic residues, and the looser structural mutation was prone to aggregation. Furthermore, the S93R mutation reduced the structural stability of beta B1-crystallin when incubated at physiological temperature and made it more sensitive to environmental stress, such as UV irradiation or oxidative stress. We also constructed a beta B1-S93R cellular model and discovered that beta B1-S93R was more sensitive to environmental stress, causing not only aggregate formation but also cellular apoptosis and impaired cellular viability. All of the results indicated that lower solubility and structural stability, sensitivity to environmental stress, vulnerability to aggregation, and impaired cellular viability of beta B1-S93R might be involved in cataract development.

Automated summary

The beta B1-S93R mutation leads to decreased solubility, increased aggregation propensity, and heightened sensitivity to environmental stress, potentially contributing to cataract development.