title: Effect of membrane mimicking environment on the conformation of a pore-forming (xSxG)6 peptide.
abstract: The mechanism of membrane interaction by beta-sheet peptides is important to understand fundamental principles of folding of beta-barrel proteins and various beta-amyloid proteins. Here, we examined the conformational characteristics of a porin-like channel forming (xSxG)(6) peptide in solution and membrane-mimicking environments (CD and ATR-IR) to understand the structural changes of the peptide during membrane association and channel formation. A comparison of the peptide conformations in different microenvironments showed that beta-sheet formation is enhanced in membrane-mimicking liposomes and SDS-micelles. The lipid-induced beta-sheet formation was confirmed by the formation of a characteristic beta-sheet structure on mixing a methanolic solution of the peptide (partially folded) with preformed liposomes. The amphipathicity of the peptide; increased hydrogen bonding, hydrophilicity, and reduction in dimensionality of the membrane surface; membrane-peptide interaction-forces; and presence of flexible glycines might facilitate beta-sheet formation in membranes. Though the CD spectra of both the peptide-bound and peptide-incorporated lipids are reminiscent of a beta-sheet structure, a significant variation in the peak positions of the two beta-sheet structures was noticed. The channel characteristics of (xSxG)(6) in the presence of low ionic strength solutions of NEt(3)BzCl and glucosammonium chloride are comparable to those reported under high ionic strength solutions. Altogether the data suggest that the channel formation by (xSxG)(6) proceeds via beta-sheet aggregate formation at the membrane surface, beta-sheet insertion, and rearrangement into a beta-barrel-like structure. The beta-barrel-like channel formation most likely arises from a sequence similarity to beta-barrel porins whereas the lipid-induced beta-sheet formation is governed by the above-mentioned factors.
authors.affiliation: Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, 46202, USA.
authors.forename: Jyothi
authors.initials: J
authors.lastname: Thundimadathil
authors.forename: Roger W
authors.initials: RW
authors.lastname: Roeske
authors.forename: Lili
authors.initials: L
authors.lastname: Guo
mesh_terms: D019840:2-Propanol / Q000737:chemistry; D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004146:Dioxanes / Q000737:chemistry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D007473:Ion Channels / Q000502:physiology; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000502:physiology; D000432:Methanol / Q000737:chemistry; D008823:Micelles; D009994:Osmolar Concentration; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D018272:Porins / Q000737:chemistry* / Q000502:physiology*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014270:Trifluoroethanol / Q000737:chemistry
chemical_list: D004146:Dioxanes; D007473:Ion Channels; D008081:Liposomes; D008565:Membrane Proteins; D008823:Micelles; D010455:Peptides; D018272:Porins; D012967:Sodium Dodecyl Sulfate; D014270:Trifluoroethanol; C025223:1,4-dioxane; D019840:2-Propanol; D000432:Methanol