Mastoparan binds to glycogen phosphorylase to regulate sarcoplasmic reticular Ca2+ release in skeletal muscle

Abstract

The ryanodine receptor, a Ca2+-releasing channel in sarcoplasmic reticulum (SR), plays an important role in the excitation—contraction coupling of skeletal muscle. In a previous study [Hirata, Nakahata and Ohizumi (2000) Mol. Pharmacol. 57, 1235—1242], we reported that mastoparan caused Ca2+ release through ryanodine receptor from the heavy fraction of SR (HSR) isolated from rabbit skeletal muscle, and that it specifically bound to a 97kDa protein which was distinct from Ca2+-pump or triadin. The present study was undertaken to identify and characterize the 97kDa mastoparan-binding protein. The 97kDa protein was purified from solubilized HSR by DEAE-Sepharose column chromatography and preparative SDS/PAGE. The partial amino acid sequence of the purified 97kDa protein was matched with that of glycogen phosphorylase (GP). The proteolytic cleavage pattern of the 97kDa protein was identical with that of GP. Furthermore, [125I-Tyr3]mastoparan specifically bound to GP. Interestingly, mastoparan-induced Ca2+ release was inhibited by exogenous addition of GP-a, and mastoparan dissociated GP from HSR. These results indicate that the 97kDa mastoparan-binding protein is GP, which negatively regulates Ca2+ release from HSR. There may be a functional cross-talk between Ca2+ release from HSR and glycogenolysis for energy supply mediated through GP in skeletal muscles.