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S Daibo, C Fukiage, Y Tamada, NE Forsberg, MK Duncan, M Azuma, TR Shearer; Crystallins Proteolyzed by Lens-Specific Calpain Lp82 Are Susceptible to Light Scattering . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4658.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Mammalian tissues contain two major classes of calpains. Ubiquitous calpains (e.g. m-calpain) may have common regulatory functions, while tissue-specific calpains (e.g. Lp82 calpain) may be more closely linked to tissue-specific functions. In young rodent lenses, proteolysis by Lp82 may be a common event during normal lens maturation and cataract formation. However, the relative contribution of Lp82 and m-calpain to proteolysis and subsequent light scattering of lens crystallins is not clear. Thus, the purpose of the present experiment was to compare calcium-induced proteolysis and light scattering of lens soluble proteins by each calpain. Methods: Transgenic (TG) mice expressing an active site mutation (Cys105Ala) in m-calpain and wild-type (WT) mice were used as sources for lenses. Total lens soluble proteins from TG or WT mice were incubated with calcium and light scattering was assayed by measuring changes in optical density. Proteolysis was detected by two-dimensional electrophoresis, and cleavage sites on proteolyzed crystallins were determined based on our previous reports. Results: Compared to WT, increased in vitro light scattering was observed in TG lens soluble proteins after incubation with calcium. The two dimensional electrophoretic patterns of soluble lens proteins from TG and WT after incubation with calcium were different. That is, a unique proteolyzed fragment from αA-crystallin produced by Lp82 accumulated in TG mice, suggesting less m-calpain activity due to the dominant negative effect of the m-calpain mutation. Conclusion: Crystallins proteolyzed by Lp82 are more susceptible to in vitro light scattering than when proteolyzed by m-calpain. This may explain why young rodent lenses with their high Lp82 activity are so susceptible to light scattering when calcium is elevated.
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