Control of the transmembrane orientation and interhelical interactions within membranes by hydrophobic helix length.
We examined the effect of the length of the hydrophobic core of Lys-flanked poly(Leu) peptides on their behavior when inserted into model membranes. Peptide structure and membrane location were assessed by the fluorescence emission lambdamax of a Trp residue in the center of the peptide sequence, the quenching of Trp fluorescence by nitroxide-labeled lipids (parallax analysis), and circular dichroism. Peptides in which the hydrophobic core varied in length from 11 to 23 residues were found to be largely alpha-helical when inserted into the bilayer. In dioleoylphosphatidylcholine (diC18:1PC) bilayers, a peptide with a 19-residue hydrophobic core exhibited highly blue-shifted fluorescence, an indication of Trp location in a nonpolar environment, and quenching localized the Trp to the bilayer center, an indication of transmembrane structure. A peptide with an 11-residue hydrophobic core exhibited emission that was red-shifted, suggesting a more polar Trp environment, and quenching showed the Trp was significantly displaced from the bilayer center, indicating that this peptide formed a nontransmembranous structure. A peptide with a 23-residue hydrophobic core gave somewhat red-shifted fluorescence, but quenching demonstrated the Trp was still close to the bilayer center, consistent with a transmembrane structure. Analogous behavior was observed when the behavior of individual peptides was examined in model membranes with various bilayer widths. Other experiments demonstrated that in diC18:1PC bilayers the dilution of the membrane concentration of the peptide with a 23-residue hydrophobic core resulted in a blue shift of fluorescence, suggesting the red-shifted fluorescence at higher peptide concentrations was due to helix oligomerization. The intermolecular self-quenching of rhodamine observed when the peptide was rhodamine-labeled, and the concentration dependence of self-quenching, supported this conclusion. These studies indicate that the mismatch between helix length and bilayer width can control membrane location, orientation, and helix-helix interactions, and thus may mismatch control both membrane protein folding and the interactions between membrane proteins.
Ren
J
J
Department of Biochemistry and Cell Biology, State University of New York at Stony Brook 11794-5215, USA.
Lew
S
S
Wang
J
J
London
E
E
D002942:Circular Dichroism; D005454:Fluorescence Polarization; D007930:Leucine / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012235:Rhodamines / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry
D008051:Lipid Bilayers; D008563:Membrane Lipids; D010455:Peptides; D012235:Rhodamines; D014364:Tryptophan; D007930:Leucine