Structures of PKA-phospholamban complexes reveal a mechanism of familial dilated cardiomyopathy

Several mutations identified in phospholamban (PLN) have been linked to familial dilated cardiomyopathy (DCM) and heart failure, yet the underlying molecular mechanism remains controversial. PLN interacts with sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and regulates calcium uptake, which is modulated by the protein kinase A (PKA)-dependent phosphorylation of PLN during the fight-or-flight response. Here, we present the crystal structures of the catalytic domain of PKA in complex with wild-type and DCM-mutant PLNs. Our structures, combined with the results from other biophysical and biochemical assays, reveal a common disease mechanism: the mutations in PLN reduce its phosphorylation level by changing its conformation and weakening its interactions with PKA. In addition, we demonstrate that another more ubiquitous SERCA-regulatory peptide, called another-regulin (ALN), shares a similar mechanism mediated by PKA in regulating SERCA activity. SignificanceDilated cardiomyopathy (DCM) is a common type of heart disease. Familial DCM is associated with mutations on phospholamban (PLN), but the mechanism remains elusive. Phosphorylation of PLN is known to influence its physiological function. We hypothesize that the connection between such mutations and DCM may involve decreased PLN phosphorylation levels due to less efficient binding to protein kinase A. We utilize x-ray crystallography, SPR, enzyme kinetic assays, thermal melt assays, and NMR to examine the structural and energetic consequences for PKA-catalyzed phosphorylation of PLN variants containing DCM-associated mutations. Our results provide a foundation to understand the general working mechanism of PKA and the physiological regulation of PLN by PKA, and also provide important insight into the pathological mechanism of DCM.