Structural basis for allosteric control of the SERCA-Phospholamban membrane complex by Ca2+ and phosphorylation
Daniel K. Weber, U. Venkateswara Reddy, Songlin Wang, Erik K. Larsen, Tata Gopinath, Martin Gustavsson, Rǎzvan L. Cornea, David D. Thomas, Alfonso De Simone, Gianluigi Veglia
Abstract
Phospholamban (PLN) is a mini-membrane protein that directly controls the cardiac Ca 2+ -transport response to β-adrenergic stimulation, thus modulating cardiac output during the fight-or-flight response. In the sarcoplasmic reticulum membrane, PLN binds to the sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA), keeping this enzyme's function within a narrow physiological window. PLN phosphorylation by cAMP-dependent protein kinase A or increase in Ca 2+ concentration reverses the inhibitory effects through an unknown mechanism. Using oriented-sample solid-state NMR spectroscopy and replica-averaged NMR-restrained structural refinement, we reveal that phosphorylation of PLN’s cytoplasmic regulatory domain signals the disruption of several inhibitory contacts at the transmembrane binding interface of the SERCA-PLN complex that are propagated to the enzyme’s active site, augmenting Ca 2+ transport. Our findings address long-standing questions about SERCA regulation, epitomizing a signal transduction mechanism operated by posttranslationally modified bitopic membrane proteins.