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Facile transition between 310- and alpha-helix: Structures of 8-, 9-, and 10-residue peptides containing the -(Leu-Aib-Ala)2-Phe-Aib- fragment

Karle, Isabella L and Flippen-Anderson, Judith L and Gurunath, R and Balaram, P (1994) Facile transition between 310- and alpha-helix: Structures of 8-, 9-, and 10-residue peptides containing the -(Leu-Aib-Ala)2-Phe-Aib- fragment. In: Protein Science, 3 (9). pp. 1547-1555.

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Abstract

A structural transition from a 310-helix to an alpha-helix has been characterized at high resolution for an octapeptide segment located in 3 different sequences. Three synthetic peptides, decapeptide (A) Boc-Aib-Trp-(Leu-Aib-Ala)2-Phe-Aib-OMe, nonapeptide (B) Boc-Trp-(Leu-Aib-Ala)2-Phe-Aib-OMe, and octapeptide (C) Boc-(Leu-Aib-Ala)2-Phe-Aib-OMe, are completely helical in their respective crystals. At 0.9 Å resolution, R factors for A, B, and C are 8.3%, 5.4%, and 7.3%, respectively. The octapeptide and nonapeptide form ideal 310-helices with average torsional angles phi(N-Calpha) and psi(Calpha-C') of –57 deg, -26 deg for C and –60 deg, -27 deg for B. The 10-residue peptide (A) begins as a 310-helix and abruptly changes to an alpha-helix at carbonyl O(3), which is the acceptor for both a 4 – 1 hydrogen bond with N(6)H and a 5 - 1 hydrogen with N(7)H, even though the last 8 residues have the same sequence in all 3 peptides. The average phi, psi angles in the decapeptide are –58 deg, -28 deg for residues 1-3 and –63 deg, -41 deg for residues 4-10. The packing of helices in the crystals does not provide any obvious reason for the transition in helix type. Fourier transform infrared studies in the solid state also provide evidence for a 310- to alpha-helix transition with the amide I band appearing at 1,656-1,657 cm-1 in the 9- and 10-residue peptides, whereas in shorter sequences the band is observed at 1,667 cm-l.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to Cold Spring Harbor Laboratory Press.
Keywords: alpha-aminoisobutyric acid peptides;helical peptide structures;helical transitions;helix packing;peptide conformation
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Date Deposited: 11 Nov 2004
Last Modified: 19 Sep 2010 04:17
URI: http://eprints.iisc.ernet.in/id/eprint/2303

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