Mapping of Sarcolipin Conformational States along the Enzymatic Pathway of SERCA

Abstract

Sarcolipin (SLN), a 31 amino acid transmembrane peptide, binds to the Sarco(endo)plasmic Reticulum Ca2+ ATPase (SERCA) decreasing its apparent Ca2+ affinity. SERCA pumps Ca2+ from the cytoplasm of muscle cells into the sarcoplasmic reticulum (SR) using energy derived from ATP hydrolysis. This re-establishes the Ca2+ gradients needed for normal muscle function. Phosphorylation of SLN relieves the inhibition of SERCA and may be involved in the beta-adrenergic response. Although a significant amount is known about SERCA, and many of the conformations throughout its transport cycle have been crystallized, the mechanism of how SLN decreases SERCA's Ca2+ affinity and alters the coupling between ATP hydrolysis and Ca2+ transport is not well understood. Using solid-state nuclear magnetic resonance spectroscopy and functional assays, we investigated the differences in the interaction of phosphorylated SLN with SERCA compared to non-phosphorylated SLN with SERCA. Previous work in our lab demonstrates that the topology of SLN in complex with SERCA changes depending on SERCA's conformation. As such, continuing work involves mapping the structural changes of phosphorylated SLN with the various conformations of SERCA. Overall, gaining a better understanding of how SERCA is regulated will add in the development of therapies for diseases resulting from improper calcium cycling.