Phosphorylation of the triadin cytoplasmic domain by CaM protein kinase inrabbit fast-twitch muscle sarcoplasmic reticulum

Skeletal muscle triadin is a sarcoplasmic reticulum (SR) membrane protein t hat had been shown to interact structurally and functionally at the cytopla smic domain (amino acid residues 1-47) with the ryanodine receptor (RyR1), and to undergo phosphorylation by endogenous calmodulin protein kinase (CaM K II) in isolated terminal cisternae from rabbit fast-twitch muscle. Here we show that triadin cytoplasmic domain expressed as glutathione-S-transfer ase fusion protein, is a substrate of the protein kinase. This finding is c orroborated by identification of a specific consensus sequence in the deduc ed amino sequence between residue 34 and 37 of triadin. Confirming the regu latory features of CaM K II, we show the phosphorylation of triadin cytopla smic segment by the kinase, when converted to the autonomous form. We propo se that triadin modulates RyR1 in a phosphorylation-dependent manner.