Cataract-causing G91del mutant destabilised βA3 heteromers formation linking with structural stability and cellular viability

Background/aims Congenital cataracts, which are genetically heterogeneous eye disorders, result in visual loss in childhood around the world. CRYBA1/BA3 serves as an abundant structural protein in the lens, and forms homomers and heteromers to maintain lens transparency. In previous study, we identified a common cataract-causing mutation, beta A3-glycine at codon 91 (G91del) (c.271-273delGAG), which deleted a highly conserved G91del and led to perinuclear zonular cataract. In this study, we aimed to explore the underlying pathogenic mechanism of G91del mutation. Methods Protein purification, size-exclusion chromatography, spectroscopy and molecular dynamics simulation assays were used to investigate the effects on the heteromers formation and the protein structural properties of beta A3-crystallin caused by G91del mutation. Intracellular beta A3-G91del overexpression, MTT (3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide) and cell apoptosis were used to investigate the cellular functions of beta A3-G91del. Results beta A3-crystallin and beta B2-crystallin could form heteromers, which have much more stable structures than beta A3 homomers. Interestingly, beta A3/beta B2 heteromers improved their resistance against the thermal stress and the guanidine hydrochloride treatment. However, the pathogenic mutation beta A3-G91del destroyed the interaction with beta B2, and thereby decreased its structural stability as well as the resistance of thermal or chemical stress. What's more, the beta A3-G91del mutation induced cell apoptosis and escaped from the protection of beta B2-crystallin. Conclusions beta A3/beta B2 heteromers play an indispensable role in maintaining lens transparency, while the beta A3-G91del mutation destabilises heteromers formation with beta B2-crystallin, impairs cellular viability and induces cellular apoptosis. These all might contribute to cataract development.

Automated summary

Congenital cataracts, a genetically heterogeneous eye disorder, can be caused by the G91del mutation in the beta A3-crystallin, affecting its heteromers formation and resistance to thermal and chemical stress, leading to impaired cellular functions and apoptosis.