title: Three-residue turns in alpha/beta-peptides and their application in the design of tertiary structures.
abstract: A new three-residue turn was serendipitously discovered in alpha/beta hybrid peptides derived from alternating C-linked carbo-beta-amino acids (beta-Caa) and L-Ala residues. The three-residue beta-alpha-beta turn at the C termini, nucleated by a helix at the N termini, resulted in helix-turn (HT) supersecondary structures in these peptides. The turn in the HT motif is stabilized by two H bonds-CO(i-2)-NH(i), with a seven-membered pseudoring (gamma turn) in the backward direction, and NH(i-2)-CO(i), with a 13-membered pseudoring in the forward direction (i being the last residue)--at the C termini. The study was extended to generalize the new three-residue turn (beta-alpha-beta) by using different alpha- and beta-amino acids. Furthermore, the HT motifs were efficiently converted, by an extension with helical oligomers at the C termini, into peptides with novel helix-turn-helix (HTH) tertiary structures. However, this resulted in the destabilization of the beta-alpha-beta turn with the concomitant nucleation of another three-residue turn, alpha-beta-beta, which is stabilized by 11- and 15-membered bifurcated H bonds. Extensive NMR spectroscopic studies were carried out to delineate the secondary and tertiary structures in these peptides, which are further supported by molecular dynamics (MD) investigations.
authors.affiliation: D-211, Discovery Laboratory, Organic Chemistry Division III, Indian Institute of Chemical Technology, Hyderabad 500 007, India. esmvee@iict.res.in
authors.forename: Gangavaram V M
authors.initials: GV
authors.lastname: Sharma
authors.forename: Pendem
authors.initials: P
authors.lastname: Nagendar
authors.forename: Kallaganti V S
authors.initials: KV
authors.lastname: Ramakrishna
authors.forename: Nagula
authors.initials: N
authors.lastname: Chandramouli
authors.forename: Madavi
authors.initials: M
authors.lastname: Choudhary
authors.forename: Ajit C
authors.initials: AC
authors.lastname: Kunwar
mesh_terms: D002942:Circular Dichroism; D003198:Computer Simulation; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D012997:Solvents; D017186:Titrimetry
chemical_list: D010455:Peptides; D012997:Solvents