Crystallins from rat lens are especially susceptible to calpain-induced light scattering compared to other species

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Abstract
To compare the susceptibility of crystallins from various animal species to formation of light scattering elements after proteolysis by calpain II enzyme (EC 3.4.22.17). Lens, total soluble proteins from: 12-day and 4-week old rat, fetal and adult bovine, 16-day embryonic and 10-week chicken, and young human cortex and nucleus were proteolyzed by either endogenous lens calpain or addition of purified calpain II for 24 h followed by incubation for up to 11 days. Absorbance of light at 405 nm estimated light scattering by crystallins; SDS-PAGE and 2D-electrophoresis assessed proteolysis on the crystallins. Most rapid light scattering occurred with total soluble proteins from young rat lens, either after adding purified calpain or by activating endogenous lens calpain with calcium. (Only rat lens showed activation of endogenous calpain II.) beta-crystallin polypeptides from rat, bovine, human, and to a more limited extent, chick lens were partially proteolyzed by addition of purified calpain II. In spite of this proteolysis, total soluble proteins from chicken, bovine, and human lenses showed no obvious light scattering by action of calpain. Crystallins from older rat lens showed approximately 50% of the light scattering displayed by crystallins from younger rats after 3 days, but only when purified calpain was added. Our results indicate an unusually high susceptibility of crystallin polypeptides from young rat lens to formation of light scattering elements after limited proteolysis. Thus, young rat lens provides a unique opportunity to investigate how properties of crystallins influence the development of light scattering found in cataract.