title: Topological stability and self-association of a completely hydrophobic model transmembrane helix in lipid bilayers.
abstract: Investigation of interactions between hydrophobic model peptides and lipid bilayers is perhaps the only way to elucidate the principles of the folding and stability of membrane proteins (White, S. H., and Wimley, W. C. (1998) Biochim. Biophys. Acta 1367, 339-352). We designed the completely hydrophobic "inert" peptide modeling a transmembrane (TM) helix without any of the specific side-chain interactions expected, X-(LALAAAA)(3)-NH(2) [X = Ac (I), 7-nitro-2-1,3-benzoxadiazol-4-yl (II), or 5(6)-carboxytetramethylrhodamine (III)]. Fourier transform infrared-polarized attenuated total reflection measurements revealed that I as well as II assume a TM helix in hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers. Dithionite quenching experiments detected no topological change (flip-flop) in the helix II for at least 24 h. Thus, the TM helix itself is a highly stable structure, even in the absence of flanking hydrophilic or aromatic amino acids which are suggested to play important roles in stable TM positioning. Helix self-association in lipid bilayers was detected by fluorescence resonance energy transfer between II and III. The peptide was in a monomer-antiparallel dimer equilibrium with an association free energy of approximately -13 kJ/mol. Electron spin resonance spectra of 1-palmitoyl-2-stearoyl-(14-doxyl)-sn-glycero-3-phosphocholine demonstrated the presence of a motionally restricted component at lower temperatures.
authors.affiliation: Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Yano
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Takemoto
authors.forename: Satoe
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yasui
authors.forename: Hiromu
authors.initials: H
authors.lastname: Sakurai
authors.forename: Wakana
authors.initials: W
authors.lastname: Ohashi
authors.forename: Miki
authors.initials: M
authors.lastname: Niwa
authors.forename: Shiroh
authors.initials: S
authors.lastname: Futaki
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sugiura
authors.forename: Katsumi
authors.initials: K
authors.lastname: Matsuzaki
mesh_terms: D008051:Lipid Bilayers / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary / Q000502:physiology*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D008051:Lipid Bilayers; D008565:Membrane Proteins; D010455:Peptides