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Title: Conformation-Specific Infrared and Ultraviolet Spectroscopy of Cold [YAPAA+H] + and [YGPAA+H] + Ions: A Stereochemical “Twist” on the β-Hairpin Turn

Incorporation of the unnatural D-proline ( DP) stereoisomer into a polypeptide sequence is a typical strategy to encourage formation of β-hairpin loops because natural sequences are often unstructured in solution. Using conformation-specific IR and UV spectroscopy of cold (≈10 K) gas-phase ions, we probe the inherent conformational preferences of the DP and LP diastereomers in the protonated peptide [YAPAA+H] +, where only intramolecular interactions are possible. Consistent with the solution-phase studies, one of the conformers of [YA DPAA+H] + is folded into a charge-stabilized β-hairpin turn. However, a second predominant conformer family containing two sequential γ-turns is also identified, with similar energetic stability. A single conformational isomer of the LP diastereomer, [YA LPAA+H] +, is found and assigned to a structure that is not the anticipated “mirror image” β-turn. Instead, the LP stereocenter promotes a cis-alanine–proline amide bond. The assigned structures contain clues that the preference of the DP diastereomer to support a trans-amide bond and the proclivity of LP for a cis-amide bond is sterically driven and can be reversed by substituting glycine for alanine in position 2, forming [YG LPAA+H] +. These results provide a basis for understanding the residue-specific and stereospecific alterations in the potential energy surfacemore » that underlie these changing preferences, providing insights to the origin of β-hairpin formation.« less
Authors:
ORCiD logo [1] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Purdue Univ., West Lafayette, IN (United States). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
FG02-00ER15105; CHE-1465028
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 15; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Purdue Univ., West Lafayette, IN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1349951
Alternate Identifier(s):
OSTI ID: 1352565