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 [YADPAA+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, [YALPAA+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 [YGLPAA+H]+. These results provide a basis for understanding the residue-specific and stereospecific alterations in the potential energy surface that underlie these changing preferences, providing insights to the origin of β-hairpin formation.
- Research Organization:
- Purdue Univ., West Lafayette, IN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
- Grant/Contract Number:
- FG02-00ER15105; CHE-1465028
- OSTI ID:
- 1349951
- Alternate ID(s):
- OSTI ID: 1352565
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Vol. 139 Journal Issue: 15; ISSN 0002-7863
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Infrared Multiphoton Dissociation Spectroscopy with Free-Electron Lasers: On the Road from Small Molecules to Biomolecules
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journal | February 2018 |
Energetic switch of the proline effect in collision-induced dissociation of singly and doubly protonated peptide Ala-Ala-Arg-Pro-Ala-Ala
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journal | December 2018 |
Intrinsic structure of pentapeptide Leu-enkephalin: geometry optimization and validation by comparison of VSCF-PT2 calculations with cold ion spectroscopy
|
journal | January 2018 |
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