title: Cloning of a muscle-specific calpain from the American lobster Homarus americanus: expression associated with muscle atrophy and restoration during moulting.
abstract: A cDNA (1977 bp) encoding a crustacean calpain (Ha-CalpM; GenBank accession no. AY124009) was isolated from a lobster fast muscle cDNA library. The open reading frame specified a 575-amino acid (aa) polypeptide with an estimated mass of 66.3 kDa. Ha-CalpM shared high identity with other calpains in the cysteine proteinase domain (domain II; aa 111-396) and domain III (aa 397-575), but most of the N-terminal domain (domain I; aa 1-110) was highly divergent. Domain II contained the cysteine, histidine and asparagine triad essential for catalysis, as well as two conserved aspartate residues that bind Ca(2+). In domain III an acidic loop in the C2-like region, which mediates Ca(2+)-dependent phospholipid binding, had an expanded stretch of 17 aspartate residues. Ha-CalpM was classified as a non-EF-hand calpain, as it lacked domain IV, a calmodulin-like region containing five EF-hand motifs. Northern blot analysis, relative reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR showed that Ha-CalpM was highly expressed in skeletal muscles, but at much lower levels in heart, digestive gland, intestine, integument, gill, nerve cord/thoracic ganglion and antennal gland. An antibody raised against a unique N-terminal sequence recognized a 62 kDa isoform in cutter claw and crusher claw closer muscles and a 68 kDa isoform in deep abdominal muscle. Ha-CalpM was distributed throughout the cytoplasm, as well as in some nuclei, of muscle fibers. Purification of Ha-CalpM showed that the 62 kDa and 68 kDa isoforms co-eluted from gel filtration and ion exchange columns at positions consistent with those of previously described Ca(2+)-dependent proteinase III (CDP III; 59 kDa). Ha-CalpM mRNA and protein did not change during the moulting cycle. The muscle-specific expression of Ha-CalpM and the ability of Ha-CalpM/CDP III to degrade myofibrillar proteins suggest that it is involved in restructuring and/or maintaining contractile structures in crustacean skeletal muscle.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Yu
authors.forename: Donald L
authors.initials: DL
authors.lastname: Mykles
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002154:Calpain / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D018978:Molting / Q000235:genetics* / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000201:enzymology / Q000235:genetics*; D008121:Nephropidae / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; D002154:Calpain