Enhances the activity of ATP2A1/SERCA1 ATPase in sarcoplasmic reticulum by displacing ATP2A1/SERCA1 inhibitors, thereby acting as a key regulator of skeletal muscle activity. Does not directly stimulate SERCA pump activity. Enhances sarcoplasmic reticulum Ca(2+) uptake and myocyte contractility by displacing the SERCA inhibitory peptides sarcolipin (SLN), phospholamban (PLN) and myoregulin (MRLN). Monomer. Interacts with ATP2A1/SERCA1.