Mitsugumin 53 Attenuates the Activity of Sarcoplasmic Reticulum Ca2+-ATPase 1a (SERCA1a) in Skeletal Muscle

Abstract

Mitsugumin 53 (MG53) is a member of membrane repair system in skeletal muscle. However, role(s) of MG53 in unique functions of skeletal muscle has not been addressed although MG53 is expressed only in skeletal and cardiac muscle. In the present study, MG53-binding proteins were searched among proteins mediating skeletal muscle contraction and relaxation using the binding assays of various MG53 domains and quadrupole time-of-flight mass spectrometry. MG53 binds to sarcoplasmic reticulum Ca2+-ATPase 1a (SERCA1a) via its tripartite motif (TRIM) and PRY domains. The binding was confirmed in rabbit skeletal muscle and mouse primary skeletal myotubes by co-immunoprecipitation and immunocytochemistry. MG53 knock-down in mouse primary skeletal myotubes increased Ca2+-uptake through SERCA1a (more than 35%) at micromolar Ca2+ but not at nanomolar Ca2+, suggesting that MG53 attenuates SERCA1a activity possibly during skeletal muscle contraction or relaxation but not during the resting state of skeletal muscle. In-silico studies suggest that the binding of MG53 to SERCA1a is mediated by unique ways compared with bindings by other proteins containing TRIM or PRY domains.