PRIMARY STRUCTURE AND TOPOLOGICAL ANALYSIS OF A SKELETAL MUSCLE-SPECIFIC JUNCTIONAL SARCOPLASMIC-RETICULUM GLYCOPROTEIN (TRIADIN)

The primary amino acid sequence for a highly abundant junctional sarco plasmic reticulum glycoprotein (triadin) has been deduced from the cDN A sequence. Based on both biochemical analysis and the predicted amino acid sequence we suggest that this protein is an intrinsic membrane g lycoprotein containing a single transmembrane domain that separates th e protein into cytoplasmic and luminal domains. The cytoplasmic domain is proposed to contain the amino-terminal 47 amino acids. The remaind er of the protein including the carboxyl terminus is proposed to be fo und within the lumen of the sarcoplasmic reticulum and contains an ext remely high concentration of basic residues. Protease analysis of inta ct triads was consistent with the topological predictions. Western and Northern blots suggest that the protein is specifically expressed in skeletal muscle and not cardiac muscle or brain. The abundance and loc alization of this protein suggest that it plays an important regulator y or structural role in excitation-contraction coupling in skeletal mu scle.