The Effects of Sarcolipin Phosphorylation on SERCA Regulation

Abstract

The Sarco(endo)plasmic Reticulum Ca2+ ATPase (SERCA) plays a major role in muscle relaxation as it uses energy from ATP hydrolysis to re-establish the Ca2+ gradients needed for normal muscle function. In skeletal muscle, this cycle is regulated by sarcolipin (SLN), a small transmembrane peptide that binds to SERCA and decreases its apparent Ca2+ affinity as well as alters the coupling between ATP hydrolysis and Ca2+ transport. This has implications for energy metabolism and thus, potential treatments for obesity. Furthermore, phosphorylation of SLN at threonine 5 relieves inhibition of SERCA, though its physiological role is not well understood. Using solid-state nuclear magnetic resonance spectroscopy, we have further characterized the structure of SLN in lipids, both phosphorylated and unphosphorylated. We have been able to fully assign the oriented spectra of SLN in lipid bilayers, which has allowed us to make residue specific conclusions about SLN structure and interactions with SERCA. Additionally, we have determined the topology of SLN and phosphorylated SLN bound to SERCA in various conformations to gain a better understanding of the mechanism of regulation.