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Title: Effect of terminal achiral and chiral residues on the conformational behaviour of poly Δ<sup>Z</sup>Phe and analysis of various interactions
Authors: Nandel, Fateh S
Kaur, Harpreet
Keywords: poly-dehydrophenylalanine
chiral amino acid
residue effect
design of peptide
Issue Date: Aug-2003
Publisher: CSIR
Abstract: Conformational properties of the peptides containing (Δ<sup>Z</sup>Phe)6 with achiral (ΔAla, Gly) and chiral (Ala, Leu) residues at both the N- and C-terminal positions have been studied with a view to design a peptide with desired helical screw sense. In all the peptides, the lowest energy conformational state corresponds to φ = 0º and Ψ = + 90ºor – 90º or both ± 90º. These structures are characterized by rise per residue of 1.94 Å; rotation per residue of 114º and 3.12 residues per turn and are stabilized by: (i) carbonyl-carbonyl interactions with the carbonyl oxygen of ith residue and carbonyl carbon atom of the carbonyl group of ith+1 residue; and (ii) N-H…π interactions between the amino group of Δ<sup>Z</sup>Phe and its own aromatic moiety. The Ala/Leu residues at the N-terminus further stabilized the structure, through C-H…π interactions with the farthest edge of the aromatic ring of ith+3 Δ<sup>Z</sup>Phe residue. For peptides Ac-L-Ala/L-Leu-(Δ<sup>Z</sup>Phe)6-NHMe, the low energy left handed helical structure (~2.5 Kcalmol-1 higher in energy) state corresponds to φ = -30º, Ψ = 120º for L-residue and φ = Ψ = 30º for Δ<sup>Z</sup>Phe residues and is in good agreement with the X-ray crystallography results for the peptide Boc-L-Ala-(Δ<sup>Z</sup>Phe)4-NHMe crystals grown from acetonitrile/ethanol mixture. Computational results suggest that the peptides Ac-D-Ala/D-Leu-(Δ<sup>Z</sup>Phe)6-NHMe adopt a right handed helical structure in polar solvents with φ = 30º, Ψ = -120º for D-residues and φ = Ψ = -30º for Δ<sup>Z</sup>Phe residues. Both in the left handed and right handed structures, the carbonyl oxygen of acetyl group is involved in 10-membered hydrogen bonded ring formation with NH of 3rd Δ<sup>Z</sup>Phe residue whereas Δ<sup>Z</sup>Pheresidues backbone adopts a 3<sub>10</sub> helix structure. Computational results also suggest that the conformational state with φ = 0º and Ψ = 90º can be realized by keeping D-Ala or D-Leu at the C-terminal. There is hardly any effect of achiral residues Gly/ΔAla on the conformational behaviour of poly-Δ<sup>Z</sup>Phe.
Description: 265-273
ISSN: 0301-1208
Appears in Collections:IJBB Vol.40(4) [August 2003]

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