Cataract-causing variant Q70P damages structural stability of βB1-crystallin and increases its tendency to form insoluble aggregates

Congenital cataract is the primary cause of childhood blindness worldwide. As the predominant structural protein, ss B1-crystallin plays an important role in maintaining lens transparency and cellular homeostasis. Numerous cataract-causing mutations of ss B1-crystallin have been identified with unclear pathogenic mechanism. We previously identified the mutation Q70P (Q to P at residue position 70) of ss B1-crystallin linked to congenital cataract in a Chinese family. In this work, we investigated the potential molecular mechanism of ss B1-Q70P in the congenital cataract at the molecular, protein, and cellular levels. We purified recombinant ss B1 wild-type (WT) and Q70P proteins and compared their structural characteristics and biophysical properties by spectroscopic experiments under physiological temperature and environmental stresses (ultraviolet irradiation, heat stress, oxidative stress). Notably, ss B1-Q70P significantly changed the structures of ss B1-crystallin and exhibited lower solubility at physiological temperature. Meanwhile, ss B1-Q70P was prone to aggregation in eukaryotic and prokaryotic cells, and was more sensitive to environmental stresses, along with impaired cellular viability. Furthermore, the molecular dynamics simulation indicated that the mutation Q70P damaged secondary structures and hydrogen bond network of ss B1-crystallin, which were essential for the first Greek-key motif. This study delineated the pathological mechanism of ss B1-Q70P and provided novel insights into treatment and prevention strategies for cataract-associated ss B1 mutations.

Automated summary

Congenital cataract is a major cause of childhood blindness worldwide. This study investigated the molecular mechanism of the ss B1-Q70P mutation in congenital cataract at the molecular, protein, and cellular levels. The study found that ss B1-Q70P significantly changed the structures of ss B1-crystallin and exhibited lower solubility, leading to cellular aggregation and impaired viability.