Purification and Characterization of Lens Specific Calpain (Lp82) from Bovine Lens

Abstract

Ubiquitous type m-calpain and lens specific Lp82 calpain were separated and partially purified from fetal bovine lens and the enzymatic characteristics were compared. Lens m-calpain required 200μM calcium for 1/2 maximal activity, while Lp82 required 30μM. Both types of calpains were inhibited by 0.1mM E64, and 5mM iodoacetamide, but not by 1mM phenylmethylsulfonyl fluoride. Lp82 was insensitive to 1μM calpastatin peptide while m-calpain was effectively inhibited. In the presence of calcium, m-calpain lost most of its activity within 2hr, while Lp82 was continually active for 18hr. Both calpains cleaved the natural substrates βA3 and αB crystallins in a similar manner. However, incubation of αA crystallin with m-calpain removed ten amino acid residues from its C-terminus, while incubation with Lp82 removed only five residues. The latter truncation product of αA was also found in vivo. These data suggested that Lp82 may have a more important role than m-calpain in modification of crystallins during lens maturation.