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2D-IR Study of a Photoswitchable Isotope-Labeled α-Helix


Backus, E H G; Bloem, R; Donaldson, P M; Ihalainen, J A; Pfister, R; Paoli, B; Caflisch, A; Hamm, P (2010). 2D-IR Study of a Photoswitchable Isotope-Labeled α-Helix. Journal of Physical Chemistry. B, 114(10):3735-3740.

Abstract

A series of photoswitchable, α-helical peptides were studied using two-dimensional infrared spectroscopy (2D-IR). Single-isotope labeling with 13C18O at various positions in the sequence was employed to spectrally isolate particular backbone positions. We show that a single 13C18O label can give rise to two bands along the diagonal of the 2D-IR spectrum, one of which is from an amide group that is hydrogen-bonded internally, or to a solvent molecule, and the other from a non-hydrogen-bonded amide group. The photoswitch enabled examination of both the folded and unfolded state of the helix. For most sites, unfolding of the peptide caused a shift of intensity from the hydrogen-bonded peak to the non-hydrogen-bonded peak. The relative intensity of the two diagonal peaks gives an indication of the fraction of molecules hydrogen-bonded at a certain location along the sequence. As this fraction varies quite substantially along the helix, we conclude that the helix is not uniformly folded. Furthermore, the shift in hydrogen bonding is much smaller than the change of helicity measured by CD spectroscopy, indicating that non-native hydrogen-bonded or mis-folded loops are formed in the unfolded ensemble.

A series of photoswitchable, α-helical peptides were studied using two-dimensional infrared spectroscopy (2D-IR). Single-isotope labeling with 13C18O at various positions in the sequence was employed to spectrally isolate particular backbone positions. We show that a single 13C18O label can give rise to two bands along the diagonal of the 2D-IR spectrum, one of which is from an amide group that is hydrogen-bonded internally, or to a solvent molecule, and the other from a non-hydrogen-bonded amide group. The photoswitch enabled examination of both the folded and unfolded state of the helix. For most sites, unfolding of the peptide caused a shift of intensity from the hydrogen-bonded peak to the non-hydrogen-bonded peak. The relative intensity of the two diagonal peaks gives an indication of the fraction of molecules hydrogen-bonded at a certain location along the sequence. As this fraction varies quite substantially along the helix, we conclude that the helix is not uniformly folded. Furthermore, the shift in hydrogen bonding is much smaller than the change of helicity measured by CD spectroscopy, indicating that non-native hydrogen-bonded or mis-folded loops are formed in the unfolded ensemble.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:18 March 2010
Deposited On:16 Dec 2010 16:15
Last Modified:05 Apr 2016 14:16
Publisher:American Chemical Society
ISSN:1520-5207
Funders:Swiss National Science Foundation, Nederlandse organisatie voor Welenschappelijk Onderzoek (NWO)
Additional Information:This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry. B, copyright © American Chemical Society after peer review and technical editing by the publisher.
Publisher DOI:10.1021/jp911849n
PubMed ID:20166694
Permanent URL: http://doi.org/10.5167/uzh-36102

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