title: Vibrational analysis of amino acids and short peptides in hydrated media. II. Role of KLLL repeats to induce helical conformations in minimalist LK-peptides.
abstract: Aqueous solution secondary structures of minimalist LK-peptides, with the generic sequence defined as KLL(KLLL)nKLLK, have been analyzed by means of circular dichroism (CD) and Raman scattering techniques. Our discussion in the present paper is mainly focused on four synthetic peptides (from 5 to 19 amino acids), KLLLK, KLLKLLLKLLK, KLLKLLLKLLLKLLK, and KLLKLLLKLLLKLLLKLLK, corresponding to the repeat unit, and to the peptide chains with the values of n = 1-3, respectively. CD and Raman spectra were analyzed in order to study both structural features of the peptide chains and their capability to form aggregates. On the basis of the obtained results it was concluded that the conformational flexibility of the shortest peptides (5-mer and 11-mer) is high enough to adopt random, beta-type, and helical chains in aqueous solution. However, the 11-mer shows a clear tendency to form beta-strands in phosphate buffer. The conformational equilibrium can be completely shifted to beta-type structures upon increasing ionic strength, i.e., in PBS and tris buffers. This equilibrium can also be shifted toward helical chains in the presence of methanol. Finally, the longest peptides (15-mer and 19-mer) are shown to form alpha-helical chains with an amphipathic character in aqueous solution. The possibility of bundle formation between helical chains is discussed over the temperature-dependent H-D exchange on labile hydrogens and particularly by considering the particular behavior of an intense Raman mode at 1127 cm-1 originating from the leucine residue side chain. The conformational dependence of this mode observed upon selective deuteration has never been documented up to now.
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: Mahmoud
authors.initials: M
authors.lastname: Ghomi
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002942:Circular Dichroism; D007930:Leucine / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D020449:Repetitive Sequences, Amino Acid; D013059:Spectrum Analysis, Raman
chemical_list: D000596:Amino Acids; D010455:Peptides; D007930:Leucine; D008239:Lysine