title: Secondary structure, orientation, and oligomerization of phospholemman, a cardiac transmembrane protein.
abstract: Human phospholemman (PLM) is a 72-residue protein, which is expressed at high density in the cardiac plasma membrane and in various other tissues. It forms ion channels selective for K+, Cl-, and taurine in lipid bilayers and colocalizes 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 homo-oligomerization. Infrared spectroscopy of proteoliposomes shows that the PLM peptide is completely alpha-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 degrees +/- 2 degrees obtained by attenuated total reflection infrared spectroscopy. Thus, our data support the idea of ion channel formation by the PLM transmembrane domain.
authors.affiliation: Department of Biological Sciences, The University of Warwick, Coventry CV4 8HE, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Beevers
authors.forename: Andreas
authors.initials: A
authors.lastname: Kukol
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D004586:Electrophoresis; D006321:Heart / Q000502:physiology; D008051:Lipid Bilayers; D008565:Membrane Proteins / Q000737:chemistry*; D008958:Models, Molecular; D010750:Phosphoproteins / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared
chemical_list: D008051:Lipid Bilayers; D008565:Membrane Proteins; D010750:Phosphoproteins; C069141:phospholemman