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Issue 16, 2016
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Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences

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Abstract

The conformational preferences of a series of short, aromatic-capped, glutamine-containing peptides have been studied under jet-cooled conditions in the gas phase. This work seeks a bottom-up understanding of the role played by glutamine residues in directing peptide structures that lead to neurodegenerative diseases. Resonant ion-dip infrared (RIDIR) spectroscopy is used to record single-conformation infrared spectra in the NH stretch, amide I and amide II regions. Comparison of the experimental spectra with the predictions of calculations carried out at the DFT M05-2X/6-31+G(d) level of theory lead to firm assignments for the H-bonding architectures of a total of eight conformers of four molecules, including three in Z-Gln-OH, one in Z-Gln-NHMe, three in Ac-Gln-NHBn, and one in Ac-Ala-Gln-NHBn. The Gln side chain engages actively in forming H-bonds with nearest-neighbor amide groups, forming C8 H-bonds to the C-terminal side, C9 H-bonds to the N-terminal side, and an amide-stacked geometry, all with an extended (C5) peptide backbone about the Gln residue. The Gln side chain also stabilizes an inverse γ-turn in the peptide backbone by forming a pair of H-bonds that bridge the γ-turn and stabilize it. Finally, the entire conformer population of Ac-Ala-Gln-NHBn is funneled into a single structure that incorporates the peptide backbone in a type I β-turn, stabilized by the Gln side chain forming a C7 H-bond to the central amide group in the β-turn not otherwise involved in a hydrogen bond. This β-turn backbone structure is nearly identical to that observed in a series of X-(AQ)-Y β-turns in the protein data bank, demonstrating that the gas-phase structure is robust to perturbations imposed by the crystalline protein environment.

Graphical abstract: Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences

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Publication details

The article was received on 16 Feb 2016, accepted on 13 Mar 2016 and first published on 17 Mar 2016


Article type: Paper
DOI: 10.1039/C6CP01062H
Citation: Phys. Chem. Chem. Phys., 2016,18, 11306-11322
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    Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences

    P. S. Walsh, J. C. Dean, C. McBurney, H. Kang, S. H. Gellman and T. S. Zwier, Phys. Chem. Chem. Phys., 2016, 18, 11306
    DOI: 10.1039/C6CP01062H

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