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Title: Conformational study of peptides containing dehydrophenylalanine Helical structures without hydrogen bond
Authors: Nandel, Fateh S
Kaur, Harpreet
Malik, Nandita
Shankar, Neelaabh
Jain, Dharam V S
Issue Date: Dec-2001
Publisher: NISCAIR-CSIR, India
Abstract: The conformational behaviour of ∆zPhe has been investigated in the model dipeptide Ac-∆z Phe-NHMe and in the model tripeptides Ac-X-∆z Phe-NHMe with X=Gly, Ala,Val, Leu, Abu, Aib and Phe and is found to be quite different. In the model tripeptides with X=Ala, Val, Leu, Abu, Phe the most stable structure corresponds to 1=-30°, ψ1= 120° and 2=ψ2 =30°. This structure is stabilized by the hydrogen bond formation between C=O of acetyl group and the NH of the amide group, resulting in the formation of a 10-membered ring but not a 310 helical structure. In the peptides Ac- Aib-∆z Phe-NHMe and Ac-(Aib-∆z Phe)3-NHMe, the helical conformers with =±30°, ψ= ±60° for Aib residue and = ψ= ±30° for ∆z Phe are predicted to be most stable. The computational studies for the positional preferences of ∆z Phe residue in the peptide containing one ∆z Phe and nine Ala residues reveal the formation of a 310 helical structure in all the cases with terminal preferences for ∆zPhe.  The conformational behaviour of Ac-(∆z Phe)n-NHMe with n≤4 is predicted to bc very labile. With n> 4, degenerate conformational states with  j, ψ values of 0° ± 90° adopt helical structures which are stabilized by carbonyl-carbonyl interactions and the N-H-π interactions between the amino group of every ∆z Phe residue with one C-C edge of its own phenyl ring. The results are in agreement with the experimental finding that screw sense of helix for peptides containing ∆z Phe residues is ambiguous in solution. The helical structures stabilized by hydrogen bond formation are found to be at least 3kCalmol-1 less stable. Conformational studies have also been carried out for the peptide Ac-(∆E Phe)6,-NHMe and the peptide Ac-∆Ala- (∆z Phe)6-NHMe containing ∆Ala residue at the N-terminal. The N-H -π interactions are absent in peptide Ac-(∆E Phe)6-NHMe.
Page(s): 417-425
ISSN: 0975-0959 (Online); 0301-1208 (Print)
Appears in Collections:IJBB Vol.38(6) [December 2001]

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