SRP-27 is a novel component of the supramolecular signaling complex involved in skeletal muscle excitation-contraction coupling
Résumé
SRP-27 is a newly identified integral membrane protein constituent of the skeletal muscle sarcoplasmic reticulum We identified its primary structure from cDNA clones isolated from a mouse skeletal muscle cDNA library. ESTs of SRP-27 were found mainly in cDNA libraries from excitable tissues of mouse. Western blot analysis confirmed the expression of SRP-27 in skeletal muscle and to a lower extent in heart and brain. Mild trypsin proteolysis combined with primary structure prediction analysis, suggest that SRP-27 has 4 transmembrane spanning alfa helices and its COOH-terminal domain faces the cytoplasmic side of the endo(sarco)plasmic reticulum. The expression of SRP-27 is higher in fast twitch skeletal muscles compared to slow twitch muscles and peaks during the first month of post-natal development. High resolution immunohistochemistry and western blot analysis of subcellular fractions indicate that SRP-27 is distributed in both longitudinal tubules and in terminal cisternae of the sarcoplasmic reticulum, as well as in the perinuclear membrane systems and the nuclear envelope of myotubes and adult fibers. SRP-27 co-sediments with the ryanodine receptor macromolecular complex in high salt sucrose gradient centrifugation, is pulled-down by anti-ryanodine receptor antibodies as well as by maurocalcin, a well characterized ryanodine receptor modulator. Our data indicate that SRP-27 is part of a sarcoplasmic reticulum supramolecular complex suggesting the involvement of SRP-27 in the structural organization or function of the molecular machinery underlying excitation-contraction coupling.
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