Role of Phospholamban Mutations in Protein-Protein Interactions

Abstract

Calcium regulation in heart muscles is achieved through a fine interplay between a variety of proteins. Of particular importance are sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) and phospholamban (PLN): SERCA transfers calcium ions against the concentration gradient and is inhibited by PLN. Inhibition is relieved upon phosphorylation of PLN at S16. Recently mutations in the pln gene have been linked to the progression of cardiomyopathies, raising questions about the biophysical basis of the disease.We have investigated the behavior of the phospholamban mutants alone and in the presence of their interaction partners through complimentary techniques. Solution NMR spectroscopy provided insights into ps-ns dynamics of the regions harboring the mutation. Oriented and magic angle spinning solid-state NMR in lipid bilayers were used to probe the topology, conformation and water accessibility of phospholamban. SERCA activity assays were performed to assess the inhibitory potency of the mutants in their native or phosphorylated forms. Such multiscale approach allowed us to build a comprehensive picture of the interactions disrupted through the mutations (Vostrikov et al. Biochim Biophys Acta 2015).Our data provides evidence that several essential regulatory functions are disrupted through the naturally occurring mutations. Amino acid substitutions or deletions lead to the alteration in the fold, conformation and dynamics of the regulatory domain of PLN. Such changes disrupt the PLN interactions with its binding partners, shifting the delicate balance of calcium ions transfer. We surmise that the development of cardiomyopathies elicited by the PLN mutants is linked to a variety of disrupted protein-protein interactions, rather than affecting one specific target.This work is supported through the American Heart Association fellowships 13POST14670054 to V.V. and 13PRE16950023 to K.S.