title: A transmembrane form of annexin XII detected by site-directed spin labeling.
abstract: Previous studies of the annexin family of Ca2+ binding proteins identified a soluble monomer in the absence of Ca2+ and a trimer adsorbed on the membrane surface in the presence of Ca2+. On the basis of site-directed spin-labeling studies of annexin XII at low pH, we now report a membrane-inserted form of the protein with a dramatically different structure. The data suggest that upon insertion a continuous transmembrane alpha-helix is reversibly formed from a helix-loop-helix motif in the solution structure. Other regions with similar membrane-insertion potential were identified in the amino acid sequence, and we propose that the corresponding helices come together to form an aqueous pore that mediates the ion channel activity reported for several annexins.
authors.affiliation: Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: R
authors.initials: R
authors.lastname: Langen
authors.forename: J M
authors.initials: JM
authors.lastname: Isas
authors.forename: W L
authors.initials: WL
authors.lastname: Hubbell
authors.forename: H T
authors.initials: HT
authors.lastname: Haigler
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017302:Annexins / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002118:Calcium; D002462:Cell Membrane / Q000648:ultrastructure; D003545:Cysteine; D004578:Electron Spin Resonance Spectroscopy; D006829:Hydra; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010718:Phosphatidylserines / Q000737:chemistry; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D013113:Spin Labels
chemical_list: D017302:Annexins; D001426:Bacterial Proteins; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D010718:Phosphatidylserines; D011994:Recombinant Proteins; C060972:SopB protein, Bacteria; D013113:Spin Labels; D003545:Cysteine; D002118:Calcium