Proteolysis by m-calpain enhances in vitro light scattering by crystallins from human and bovine lenses.

Objective: To determine if proteolysis by the calcium-activated protease m-calpain (EC 34.22.17) enhances in vitro light scattering in crystallins from human and bovine lenses.

Methods: Total soluble proteins from bovine, human, and rodent lenses, betaH crystallin, or recombinant betaB1 polypeptide were pre-incubated in the presence or absence of activated m-calpain. Heat-induced light scattering was assayed by measuring changes in optical density at 405 nm. Proteolysis and cleavage sites were detected by SDS-PAGE, two dimensional electrophoresis, and N-terminal Edman sequencing.

Results: The in vitro cleavage sites produced by m-calpain on the N-termini of human betaB1, betaA3, and betaB2-crystallins were similar to some of those on bovine and rat crystallins. Proteolysis of alpha- and beta-crystallins was associated with enhanced, heat-induced light scattering by human and bovine lens proteins.

Conclusions: Proteolysis may be a contributing factor in the insolubilization of crystallins occurring during normal maturation of lens or during cataract formation in such species as man and cows.