β‐Crystallins insolubilized by calpain II in vitro contain cleavage sites similar to β‐crystallins insolubilized during cataract

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Abstract
Incubation of soluble proteins from rat lens with the protease calpain II caused the precipitation of β-crystallin polypeptides. Two-dimensional electrophoresis and sequence analysis identified β-crystallin polypeptides both before and after their precipitation by calpain II. β-crystallin polypeptides precipitated by calpain were cleaved at their NH2-terminal extensions. These cleavage sites were similar to cleavage sites occurring in β-crystallin polypeptides precipitated during formation of experimental cataract induced by an overdose of selenite. These data suggested that calpain II caused β-crystallin insolubilization during cataract formation, and indicated that the process can be mimicked in vitro.