Molecular cloning of the cDNA encoding human skeletal muscle triadin and its localisation to chromosome 6q22-6q23

We have cloned and sequenced the cDNA encoding triadin, a junctional terminal cisternae protein from human skeletal muscle. The cDNA, 2941 base pairs in length, encodes a protein of 729 amino acids with a predicted molecular mass of 81,545 Da. Hydropathy analysis indicates that triadin of human skeletal muscle has the same topology in the myoplasmic, transmembrane and sarcoplasmic reticulum luminal domains as that of triadin from rabbit skeletal muscle. The number and relative position of potential modulation sites are also conserved between the human and rabbit proteins. The cDNA sequence of the predicted sarcoplasmic reticulum luminal domain of human triadin diverged from that of rabbit, with an observed similarity of 82%, translating to an identity of 77% in amino acid sequence. Two insertions of 9 and 12 residues in the amino acid sequence were observed in the predicted luminal domain of triadin, although the structural and functional consequences of such insertions are expected to be minimal. Using fluorescence in situ hybridisation, we have assigned the gene encoding human triadin to the long arm of chromosome 6 in the region 6q22-6q23. Our structural analysis of human triadin supports a central role for this protein in the mechanism of skeletal muscle excitation/contraction coupling.