期刊
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 18, 期 16, 页码 11306-11322出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/c6cp01062h
关键词
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资金
- National Science Foundation [CHE-1213289]
- NSF [CHE-1307365]
- National Research Foundation of Korea (NRF) - Ministry of Education [NRF-2013R1A1A2008708]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1565810, 1465028, 1307365] Funding Source: National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1213289] Funding Source: National Science Foundation
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 gamma-turn in the peptide backbone by forming a pair of H-bonds that bridge the gamma-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 beta-turn, stabilized by the Gln side chain forming a C7 H-bond to the central amide group in the beta-turn not otherwise involved in a hydrogen bond. This beta-turn backbone structure is nearly identical to that observed in a series of X-(AQ)-Y beta-turns in the protein data bank, demonstrating that the gas-phase structure is robust to perturbations imposed by the crystalline protein environment.
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