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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
Author(s):DeBlase, Andrew F
Contributor(s):Zwier, Timothy S.; McLuckey, Scott A; Burke, Nicole L; Lawler, John T; Harrilal, Christopher P
Subject(s):Ions
Abstract:Incorporation of the unnatural D-proline ($^{D}$P) stereoisomer into a polypeptide sequence is a typical strategy to encourage formation of $beta$-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 $^{D}$P and $^{L}$P 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 $beta$-hairpin turn. However, a second predominant conformer family containing two sequential $gamma$-turns is also identified, with similar energetic stability. A single conformational isomer of the $^{L}$P diastereomer, [YALPAA+H]$^{+}$, is found and assigned to a structure that is not the anticipated “mirror image” $beta$-turn. Instead, the $^{L}$P stereo center promotes a cis alanine-proline amide bond. The assigned structures contain clues that the preference of the $^{D}$P diastereomer to support a trans-amide bond and the proclivity of $^{L}$P 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 stereo-specific alterations in the potential energy surface that underlie these changing preferences, providing insights to the origin of $beta$-hairpin formation.
Issue Date:6/23/2017
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/97149
DOI:10.15278/isms.2017.FE04
Date Available in IDEALS:2017-07-27


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