title: Vibrational analysis of amino acids and short peptides in hydrated media. 3. Successive KL repeats induce highly stable beta-strands capable of forming non-H-bonded aggregates.
abstract: Circular dichroism (CD) and Raman scattering were applied to the aqueous solution of minimalist LK peptides constructed with successive KL repeats leading to the following generic primary sequence: (KL)nK. Three peptides of this family, a 3-mer (n=1), a 9-mer (n=4), and a 15-mer (n=7), are analyzed in this report. Raman spectra of the 3-mer (KLK, a random chain) and its labile-hydrogen deuterated species yield a set of interesting information for analyzing longer peptides of this series. Although the CD spectrum of the 9-mer (KLKLKLKLK) reveals a signal traditionally assigned to a random structure, the corresponding Raman spectrum allows finding a mixture of conformations in solution, adopting predominantly beta-type structures. This fact proves the utility of Raman spectroscopy to eliminate eventual ambiguity concerning conformational assignments in peptides based only on the use of CD technique. Finally, the 15-mer (KLKLKLKLKLKLKLK) gives rise to CD and Raman spectra clearly assignable to a beta-type structure. On the basis of all the observed results on the 15-mer, we can confirm that this peptide may exist as isolated beta-strands at low concentration (sub-micromolar), flat-oriented at the air/water interface, whereas at high concentrations (millimolar), non-H-bonded immersible aggregates might be formed. A hypothetical model for these beta-strand aggregates could be proposed as stabilized by an interior hydrophobic core and a hydrophilic external face, formed by leucine and lysine side chains, respectively.
authors.affiliation: UMR CNRS 7033, BioMoCeTi, UFR SMBH, Université Paris 13, 74 rue Marcel Cachin, 93017 Bobigny cedex, France.
authors.forename: Guy
authors.initials: G
authors.lastname: Guiffo-Soh
authors.forename: Belén
authors.initials: B
authors.lastname: Hernandez
authors.forename: Yves-Marie
authors.initials: YM
authors.lastname: Coïc
authors.forename: Fatima-Zohra
authors.initials: FZ
authors.lastname: Boukhalfa-Heniche
authors.forename: Giulia
authors.initials: G
authors.lastname: Fadda
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Ghomi
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D001483:Base Sequence; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D010455:Peptides / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D010455:Peptides; D014867:Water