Sarcolipin interaction with SERCA is distinct from Phospholamban; only Sarcolipin can promote uncoupling of the SERCA pump (LB244)

Abstract

Sarcolipin (SLN) and Phospholamban (PLB) modulate the activity of the Sarco‐Endoplasmic Reticulum Ca2+ ATPase (SERCA) pump, in cardiac and skeletal muscle. Recent data suggest that SLN could play a role in muscle thermogenesis by promoting the uncoupling of SERCA ATP hydrolysis activity from its Ca2+ transport function. However, the mechanistic details of this uncoupling are unknown. In order to define how SLN promotes uncoupling of SERCA, we compared the interaction of SLN and SERCA1, with that of PLB. We used the cross‐linker (1, 6‐bismaleimidohexane (BMH)) to detect dynamic protein interaction during the SERCA cycle. We also performed Ca2+ uptake and ATP hydrolysis assays to study the effect of SLN on SERCA. Our studies reveal that 1) SLN affects the Vmax of SERCA Ca2+ uptake but not the pump affinity for Ca2+ 2) SLN can bind to SERCA in the presence of high [Ca2+] whereas PLB can only interact with the ATP bound, Ca2+ free E2 state and 3) unlike PLB, SLN interacts with SERCA throughout the kinetic cycle and promotes uncoupling of the SERCA pump. Using SERCA transmembrane mutants we additionally show that PLB and SLN can bind to the same groove but interact with different residues on SERCA. These data suggest that SLN is functionally distinct from PLB; its ability to interact with SERCA in the presence of Ca2+ causes uncoupling of the SERCA pump and increased heat production.Grant Funding Source: Supported by NIH and AHA