title: Homooligomeric β3(R)-valine peptides: Transformation between C14and C12helical structures induced by a guest Aib residue.
abstract: Novel helical, structures unprecedented in the chemistry of α-polypeptides, may be found in polypeptides containing β and γ amino acids. The structural characterization of C12and C14-helices in oligo β-peptides was originally achieved using conformationally constrained cyclic β-residues. This study explores the conformational characteristics of proteinogenic β3residues in homooligomeric sequences and addresses the issue of inducing a transition between C14and C12helices by the introduction of a guest α-residue. Folded C14-helical structures are demonstrated for the nonapeptide Boc-[β3(R)Val]9-OMe by NMR methods in CDCl3-DMSO mixtures, while the peptide was found to be aggregated in CDCl3. The insertion of a guest Aib residue into an oligo-β-valine sequence in the octapeptide model Boc-[(β3(R)Val)3-Aib-(β3(R)Val]4-OMe results in well dispersed NH region in the NMR spectrum indicating folded structures in CDCl3. Structure calculations for both the peptides using NOE distance constraints support a C14helical structure in the homooligomer which transform into a C12helix on introduction of the guest Aib residue.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Basavalingappa
authors.initials: B
authors.lastname: Vasantha
authors.affiliation: Department of Physics, NMR Research Center, Indian Institute of Science, Bangalore, 560012, India.
authors.forename: Gijo
authors.initials: G
authors.lastname: George
authors.affiliation: NMR Research Center, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Srinivasarao
authors.initials: S
authors.lastname: Raghothama
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560 012, India.
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012997:Solvents / Q000737:chemistry; D014633:Valine / Q000737:chemistry*
chemical_list: D010455:Peptides; D012997:Solvents; D014633:Valine
keywords: C12-helix; C14-helix; β-peptide conformation; β3(R)valine; β3-peptides