Lp82 is the dominant form of calpain in young mouse lens

The purpose of this study was to characterize Lp82 calpain in normal mouse. Lp82 is a lens-specific, calcium-activated isozyme from the calpain super family of cysteine proteases (EC 34.22.17), RT-PCR and molecular cloning we re performed on total RNA from 12 day-old mice. Lp82 and m-calpain protein Levels and proteolytic activities in lenses were measured by casein zymogra phy, immunoblotting, and ELISA after partial purification by DEAE-HPLC. The 2334-bp cDNA encoding for mouse Lp82 contained a single large open read ing frame encoding a protein of 709 amino acid residues with a calculated m olecular weight of 82.2 kDa and a predicted pi of 5.8 The amino acid sequen ce of mouse lens Lp82 was 99% homologous to rat lens Lp82. As in rat, mouse lens Lp82 showed a unique N-terminus and deletion of the IS1 and IS2 regio ns. In contrast to rat, Lp82 was the dominant calpain in young mouse lens. Lp82 was lens-specific, and the lens nucleus contained the highest specific activity of Lp82 and very little m-calpain. Endogenous Lp82 in lens solubl e proteins was activated by addition of calcium and caused limited proteoly sis of crystallins even in the presence of large amounts of recombinant dom ain I from the natural calpain inhibitor calpastatin. Loss of Lp82 protein accompanied aging of mouse lens. Lp82 may be responsible for a major portio n of crystallin proteolysis occurring during normal lens development and ma turation, or during cataract formation in young mice. (C) 1999 Academic Pre ss.