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  • Title: Stabilization of a novel beta-turn-like motif by nonconventional intramolecular hydrogen-bonding interactions in a model peptide incorporating beta-alanine.
    Author: Thakur AK, Kishore R.
    Journal: Biopolymers; 2000 May; 53(6):447-54. PubMed ID: 10775060.
    Abstract:
    The chemical synthesis and x-ray crystal structure analysis of a model peptide incorporating a conformationally adaptable unsubstituted beta-Ala residue: Boc-beta-Ala-Acc6-OCH3 (C16H28N2O5, molecular weight = 328.41; 1) has been described. The peptide crystallized in the space group P2(1)2(1)2(1) a = 8.537 (3), b = 8.872 (10), c = 25.327 (8), alpha = beta = gamma = 90.0 degrees, Z = 4. An attractive feature of the crystal structure analysis of 1 is an accommodation of a significantly folded beta-Ala residue in a short linear peptide. The overall peptide conformation is typically folded into a beta-turn-like motif. The stabilization of the peptide backbone conformation by nonconventional C-H...O weak intramolecular hydrogen-bonding interactions, involving the ester terminal carbon atom and the ethereal oxygen of the Boc group, has been evoked. The conformational constraint that seems most apparent is the phi, psi value of the highly constrained hydrophobic Acc6 ring that may play a key role in inducing or sustaining the observed pseudo type III or III' beta-turn structure. The resulting 12-membered hydrogen bonding ring motif in 1 is distinctly different from the one found in classical beta-turn structures, stabilized by a conventional strong C=O...H-N intramolecular hydrogen bond, comprised of alpha-amino acids. The potential of the conformationally adaptable beta-Ala residue to occupy i + 1 position (left corner) of the folded beta-turn-like structure and to design and construct novel secondary structural features have been emphasized.
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