Disulfide cross-links in the interaction of a cataract-linked αA-crystallin mutant with βB1-crystallin

A number of αA-crystallin mutants are associated with hereditary cataract including cysteine substitution at arginine 49. We report the formation of affinity-driven disulfide bonds in the interaction of αA-R49C with βB1-crystallin. To mimic cysteine thiolation in the lens, βB1-crystallin was modified by a bimane probe through a disulfide linkage. Our data suggest a mechanism whereby a transient disulfide bond occurs between αA- and βB1-crystallin followed by a disulfide exchange with cysteine 49 of a neighboring αA-crystallin subunit. This is the first investigation of disulfide bonds in the confine of the chaperone/substrate complex where reaction rates are favored by orders of magnitude. Covalent protein cross-links are a hallmark of age-related cataract and may be a factor in its inherited form.