Topological stability and self-association of a completely hydrophobic model transmembrane helix in lipid bilayers.
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.
Yano
Yoshiaki
Y
Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
Takemoto
Tomokazu
T
Kobayashi
Satoe
S
Yasui
Hiroyuki
H
Sakurai
Hiromu
H
Ohashi
Wakana
W
Niwa
Miki
M
Futaki
Shiroh
S
Sugiura
Yukio
Y
Matsuzaki
Katsumi
K
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
D008051:Lipid Bilayers; D008565:Membrane Proteins; D010455:Peptides