A protein complex found as a homopentamer of the phospholamban (PLN) protein in the sarcoplasmic reticulum (SR) membrane of cardiomyocytes. Cardiac PLN is a main determinant of muscle contraction and relaxation, by regulating intracellular calcium levels.
Comment:
An example of this is PLN in human (UniProt symbol P26678) in PMID:16043693 (inferred from direct assay).