Elucidating the Uncoupling of ATP Hydrolysis and Ca2+ Transport in SERCA by Sarcolipin

Abstract

The activity of the sarco(endo)plasmic reticulum Ca2+ -ATPase (SERCA), which plays a key role in muscle contraction and relaxation, is regulated by sarcolipin (SLN), a 31-residue transmembrane peptide. Sarcolipin has been shown to uncouple ATP hydrolysis and Ca2+ transport in SERCA and is largely found in skeletal muscle and the atria of the heart. The interaction between SLN and SERCA is thought to play an important role in energy metabolism. SLN is composed of a transmembrane helix flanked by two short, unstructured N- and C-termini. The N-terminus is hypothesized to play a role in the uncoupling of SERCA, while the role of the C-terminus has been shown to be largely responsible for SERCA inhibition. In this study, we made two constructs of SLN, with either the C- or N-terminus deleted. We then used coupled-enzyme activity assays to measure the effect of the SLN constructs on SERCA ATPase activity and isothermal titration calorimetry (ITC) to monitor the change in heat release due to ATP hydrolysis. We found through these methods that the deletion of the termini led effected the uncoupling function in SLN. The results of this study, in combination with forthcoming solid-state NMR studies, will help to establish the mechanism by which SLN regulates SERCA activity.