Spectroscopic studies of phospholamban variants in phospholipid bilayers.

Phospholamban (PLB) is a 52 amino acid transmembrane protein found in the sarcoplasmic reticulum of cardiac myocytes, where it regulates the transport of calcium ions by SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase). This work has shown that the cytoplasmic domain of PLB associates with phospholipid vesicles, possibly with the lipid polar head groups, and, in doing so, undergoes a transition from a random coil to a more helical conformation. These findings support a recent hypothesis that the cytoplasmic domain of PLB acts as a conformational switch, alternating between an orientation that lies across the membrane surface and an upright orientation that associates with the regulatory site of SERCA.