Secondary structure, orientation and oligomerisation of phospholemman, a cardiac transmembrane protein

Abstract – Human Phospholemman (PLM) is a 72 residue protein, which is expressed at high density in the cardiac plasmamembrane and in various other tissues. It forms ion channels selective for K+, Cl- and taurine in lipid bilayers and co-localises with the Na+/K+ ATPase and the Na+/Ca2+ exchanger, which may suggest a role in the regulation of cell volume. Here we present the first structural data based on synthetic peptides representing the transmembrane domain of PLM. Perfluoro-octaneoate-PAGE of reconstituted proteoliposomes containing PLM reveals a tetrameric homooligomerisation. Infrared spectroscopy of proteoliposomes shows that the PLM peptide is completely α-helical even beyond the hydrophobic core residues. Hydrogen/deuterium exchange experiments reveal that a core of 20 – 22 residues is not accessible to water, thus embedded in the lipid membrane. The maximum helix tilt is (17±2)º obtained by attenuated total reflection infrared spectroscopy. Thus our data supports the idea of ion channel formation by the PLM transmembrane domain