Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2000
Publication Date: N/A
Interpretive Summary: The primary determinant of meat tenderness is the extent of proteolytic breakdown of muscle fiber that occurs during the post-slaughter aging period. A calcium-dependent protease called mucalpain, a product of the CAPN1 gene, is the primary enzyme involved with this breakdown. This appears to be the reason that calcium injection of meat increases tenderization. In order to support research for the role of CAPN1 in meat tenderization in pork, we have obtained the sequence of the mRNA coding for the mucalpain protein. During this process, it was discovered that two distinct forms of CAPN1 can be detected, one in embryonic tissue and one in adult tissue. Further study suggested that one form is relatively rare and is not expressed in all swine. However, this study suggests that it is unlikely that the rare form plays an important role in determining meat tenderness.
Technical Abstract: The calpain family of genes encode cysteine proteases that have been implicated in processes such as regluation of protein kinases and hormone receptors, cytoskeletal reorganization, cell cycle progression, and apoptosis. The active enzyme includes a small subunit that appears to be shared by all the large subunit gene family. CAPN1 is a ubiquitous calpain that requires micromolar levels of calcium for proteolytic activity in vitro. It appears to be the major enzyme involved in postmortem tenderization of beef, and has recently been identified as a positional candidate gene for a quantitative trait locus (QTL) affecting meat tenderness in cattle. Human, mouse, and cattle CAPN1 cDNA clones have been described, each predicting proteins with four domains. Domain IV contains four motifs with homology to the calcium-binding portions of calmodulin, as well as residues involved with contacting the small subunit. The cDNA coding for porcine CAPN1 was cloned from two pooled-tissue libraries, one made from adult tissues and one from embryonic tissue. The isoform isolated from the embryonic library showed evidence of a retained intron that would predict a truncated protein lacking two of the four calcium binding motifs of Domain IV, and would likely be deficient in binding the small subunit. Expression of this variant form appears to be limited to early embryonic tissue from swine with Meishan germplasm, and therefore does not appear to be required for normal development.