βA4-Crystallin Mutations Disrupt Structural Stability and Crystallin Interactions in Congenital Cataract Pathogenesis.

PURPOSE: Mutations in the crystallin beta A4 (CRYBA4) gene, which encodes βA4-crystallin, are associated with congenital cataract; yet, the underlying pathogenic mechanisms remain elusive. We systematically investigated four cataract-associated βA4-crystallin mutants (βA4-Y67N, βA4-L69P, βA4-F94S, and βA4-G147V), each representing distinct structural contexts, to assess their effects on structural destabilization and interactions with key crystallins.

METHODS

We employed a comprehensive approach, including protein expression and purification, size-exclusion chromatography, crosslinking, and circular dichroism spectroscopy, to evaluate the polymerization propensity, structural integrity, and stability of the proteins. Additionally, antibiotic resistance screening and yeast two-hybrid assays were used to examine the impact of these mutations on protein folding and interactions between proteins.

RESULTS

Our findings reveal that core mutations (βA4-L69P/βA4-F94S) induce severe aggregation and disrupt interactions with βB1- and βB2-crystallin, the inter-motif mutation (βA4-G147V) reduces protein flexibility, and the surface mutation (βA4-Y67N) results in mild disruption of protein interactions. Notably, αA-crystallin preferentially stabilizes core mutants but exhibits limited effects on others.

CONCLUSIONS

The present study revealed mutations in βA4-crystallin-driven cataractogenesis via distinct mechanisms according to their distinct structural contexts. αA-crystallin functions as a primary mitigator of severe misfolding, preferentially stabilizing aggregation-prone conformers. These findings suggest that mutation-specific stabilization via small-molecule chaperones or enhanced αA-crystallin activity may represent potential precision therapeutic strategies for βA4-crystallin-associated congenital cataracts.