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 Title: CHARACTERIZING PEPTIDE β-HAIRPIN LOOPS VIA COLD ION SPECTROSCOPY OF MODEL COMPOUNDS Author(s): Lawler, John T. Contributor(s): Zwier, Timothy S.; McLuckey, Scott A.; Fischer, Joshua L.; Harrilal, Christopher P.; DeBlase, Andrew F. Subject(s): Ions Abstract: The introduction of non-native D-amino acids into peptides is known to reduce conformational entropy in peptides. D-proline has been shown to promote the formation of $beta$-hairpin loops when paired with Gly, providing a framework for building these loops with different lengths of anti-parallel beta-sheet. This study seeks to characterize and compare the conformational preferences of a model protonated pentapeptide containing DPG, [YAP$^{D}$GA+H]$^{+}$, with its L-Pro counterpart via conformation specific cold ion spectroscopy as a foundation for future consideration of larger beta-hairpin models._x000d_ _x000d_ The UV spectrum of YAP$^{D}$GA of the Tyr chromophore is beautifully sharp, but contains a complicated set of transitions that could arise from the presence of more than one conformer. To assess this possibility, we recorded non-conformation specific IR “gain” spectra in the hydride stretch region. The IR spectrum so obtained displays a set of five strong IR transitions that bear a close resemblance to those found in one of the conformers of its close analog, [YAP$^{D}$AA+H]$^{+}$, signaling that a single conformer dominates the population. Two transitions at 3392 and 3464 cm-1 are slightly shifted versions of the C10 and C14 hydrogen bonds found in one of the conformers of [YAP$^{D}$AA+H]$^{+}$, and are characteristic of formation of a $beta$-hairpin loop. Notably, in [YAP$^{D}$GA+H]$^{+}$, there is at most a minor second conformer with a free carboxylic acid OH, appearing weakly in the IR “gain” spectrum. As expected, the UV spectrum of YAP$^{L}$GA is more congested, which suggests the presence of multiple conformers. Further investigation into this peptide will reveal the conformational preferences of the L-pro containing molecule. Preliminary data affirms that D-proline containing peptides show reduced conformational states when compared to their natural counterparts. _x000d_ 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/2142/96939 DOI: 10.15278/isms.2017.FE06 Date Available in IDEALS: 2017-07-272018-01-29
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