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|Title:||Effect of terminal achiral and chiral residues on the conformational behaviour of poly ΔZPhe and analysis of various interactions|
|Authors:||Nandel, Fateh S|
|Keywords:||poly-dehydrophenylalanine;conformation;chiral amino acid;residue effect;design of peptide;interactions|
|Abstract:||Conformational properties of the peptides containing (ΔZPhe)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 ΔZPhe 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 ΔZPhe residue. For peptides Ac-L-Ala/L-Leu-(ΔZPhe)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 ΔZPhe residues and is in good agreement with the X-ray crystallography results for the peptide Boc-L-Ala-(ΔZPhe)4-NHMe crystals grown from acetonitrile/ethanol mixture. Computational results suggest that the peptides Ac-D-Ala/D-Leu-(ΔZPhe)6-NHMe adopt a right handed helical structure in polar solvents with φ = 30º, Ψ = -120º for D-residues and φ = Ψ = -30º for ΔZPhe 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 ΔZPhe residue whereas ΔZPheresidues backbone adopts a 310 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-ΔZPhe.|
|Appears in Collections:||IJBB Vol.40(4) [August 2003]|
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