title: Organization of diphtheria toxin T domain in bilayers: a site-directed spin labeling study.
abstract: The diphtheria toxin transmembrane (T) domain was spin-labeled at consecutive residues in a helical segment, TH9. After binding of the T domain to membranes at low pH, the nitroxide side chains generated by spin labeling were measured with respect to their frequency of collision with polar and nonpolar reagents. The data showed that the helical structure of TH9 in solution is conserved, with one face exposed to water and the other to the hydrophobic interior of the bilayer. Measurement of the depth of the nitroxide side chains from the membrane surfaces revealed an incremental change of about 5 angstroms per turn, which is consistent with a transmembrane orientation of an alpha helix. These results indicate that the helix forms the lining of a transmembrane water-filled channel.
authors.affiliation: Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-7008, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Oh
authors.forename: H
authors.initials: H
authors.lastname: Zhan
authors.forename: C
authors.initials: C
authors.lastname: Cui
authors.forename: K
authors.initials: K
authors.lastname: Hideg
authors.forename: R J
authors.initials: RJ
authors.lastname: Collier
authors.forename: W L
authors.initials: WL
authors.lastname: Hubbell
mesh_terms: D000595:Amino Acid Sequence; D004167:Diphtheria Toxin / Q000737:chemistry* / Q000235:genetics; D004492:Edetic Acid / Q000031:analogs & derivatives; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009532:Nickel; D010100:Oxygen; D010743:Phospholipids; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013113:Spin Labels
chemical_list: D004167:Diphtheria Toxin; D008051:Lipid Bilayers; D010743:Phospholipids; D013113:Spin Labels; C026058:EDDA; D009532:Nickel; D004492:Edetic Acid; D010100:Oxygen