Cataract-causing variant G119R impaired the oligomeric homeostasis of βB2-crystallin with lower structural stability and more sensitivity to the environmental stress.

Congenital cataract is a significant cause of blindness in children, primarily associated with genetic factors. βB2-crystallin, the principal structural protein of the lens, is essential for preserving lens transparency and stabilizing the intracellular environment. Numerous mutations in βB2-crystallin are identified as contributors to cataract; however, the underlying pathogenic mechanisms remain unclear. Our study focused on a Chinese family with a new G119R mutation associated with congenital nuclear cataract, investigating the molecular mechanism of βB2-G119R in the pathogenesis of congenital cataracts at the protein, cellular, and molecular levels. We purified the mutant protein and analyzed its structural changes using size-exclusion chromatography (SEC), fluorescence spectroscopy, and circular dichroism (CD) spectroscopy. As a result, this mutation disrupted the oligomerization balance of βB2-crystallin and reduced both its structural and thermal stability. Furthermore, the mutant protein exhibited decreased resistance under the environmental stress, which was confirmed by the cell model demonstrating heightened sensitivity to the stress. Additionally, molecular dynamics simulation results indicated that the G119R mutation adversely affected the advanced structure of βB2-crystallin. Consequently, our findings underscored the importance of G119 in maintaining the structural stability of crystallin, offering new insights for further investigation into the pathogenesis of cataracts.