Dystrophin and the membranehypothesis of muscular dystrophy

Abstract

Calpains are calcium regulated proteases involved in cellular functions that include muscle proteolysis both ante- and postmortem. Here, we describe the molecular characterization of the rainbow trout catalytic subunits of the μ- and m-calpains, respectively. The cDNA sequence for Capn1 encodes a protein of 704 amino acids with a calculated molecular mass of 79.9 kDa. The amino acid sequence shows 66% and 86% identity with the mouse and zebrafish Capn1, respectively. The Capn2 cDNA codes for a protein consisting of 701 amino acid residues with a calculated molecular mass of 78.2 kDa. The protein shows 65% amino acid sequence identity with the mouse and chicken Capn2. The two isozymes of rainbow trout have the characteristic domains: I (propeptide), II (cysteine catalytic site), III (electrostatic switch), and IV (contains five EF-hands). Because starvation induces muscle wasting, the hypothesis of this study was that starvation could affect regulation of the calpain system in muscle. Starvation of rainbow trout fingerlings (15–20 g) for 35 days stimulated the expression of Capn1 (2.2-fold increase, P<0.01), Capn2 (6.0-fold increase, P<0.01), and calpastatins (1.6-fold increase, P<0.05) as measured by quantitative real-time RT-PCR. The mRNA changes led to a 1.23-fold increase in the calpain catalytic activity. The results suggest a potential role of calpains in protein mobilization as a source of energy under fasting condition.