title: Transmembrane peptides stabilize inverted cubic phases in a biphasic length-dependent manner: implications for protein-induced membrane fusion.
abstract: WALP peptides consist of repeating alanine-leucine sequences of different lengths, flanked with tryptophan "anchors" at each end. They form membrane-spanning alpha-helices in lipid membranes, and mimic protein transmembrane domains. WALP peptides of increasing length, from 19 to 31 amino acids, were incorporated into N-monomethylated dioleoylphosphatidylethanolamine (DOPE-Me) at concentrations up to 0.5 mol % peptide. When pure DOPE-Me is heated slowly, the lamellar liquid crystalline (L(alpha)) phase first forms an inverted cubic (Q(II)) phase, and the inverted hexagonal (H(II)) phase at higher temperatures. Using time-resolved x-ray diffraction and slow temperature scans (1.5 degrees C/h), WALP peptides were shown to decrease the temperatures of Q(II) and H(II) phase formation (T(Q) and T(H), respectively) as a function of peptide concentration. The shortest and longest peptides reduced T(Q) the most, whereas intermediate lengths had weaker effects. These findings are relevant to membrane fusion because the first step in the L(alpha)/Q(II) phase transition is believed to be the formation of fusion pores between pure lipid membranes. These results imply that physiologically relevant concentrations of these peptides could increase the susceptibility of biomembrane lipids to fusion through an effect on lipid phase behavior, and may explain one role of the membrane-spanning domains in the proteins that mediate membrane fusion.
authors.affiliation: Givaudan Inc., Cincinnati, Ohio, USA. david.siegel@givaudan.com
authors.forename: D P
authors.initials: DP
authors.lastname: Siegel
authors.forename: V
authors.initials: V
authors.lastname: Cherezov
authors.forename: D V
authors.initials: DV
authors.lastname: Greathouse
authors.forename: R E
authors.initials: RE
authors.lastname: Koeppe
authors.forename: J Antoinette
authors.initials: JA
authors.lastname: Killian
authors.forename: M
authors.initials: M
authors.lastname: Caffrey
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008081:Liposomes; D008561:Membrane Fusion; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D044367:Phase Transition; D010714:Phosphatidylethanolamines / Q000737:chemistry; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017356:Synchrotrons; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: C410262:1,2-dioleoyl-glycero-3-phosphatidyl ethanolamine; D000596:Amino Acids; D008051:Lipid Bilayers; D008055:Lipids; D008081:Liposomes; D010455:Peptides; D010714:Phosphatidylethanolamines; D011506:Proteins; D011993:Recombinant Fusion Proteins