2D-IR study of a photoswitchable isotope-labeled alpha-helix

Title2D-IR study of a photoswitchable isotope-labeled alpha-helix
Publication TypeJournal Article
Year of Publication2010
AuthorsBackus E.HG, Bloem R., Donaldson P.M, Ihalainen J.A, Pfister R., Paoli B., Caflisch A., Hamm P.
JournalThe Journal of Physical Chemistry B
Date Published2010 Mar 18
Type of ArticleResearch Article
KeywordsAmino Acid Sequence, Carbon Isotopes, Circular Dichroism, Hydrogen Bonding, Isotope Labeling, Oxygen Isotopes, Peptides, Protein Folding, Protein Structure, Secondary, Spectrophotometry, Infrared

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.



Alternate JournalJ. Phys. Chem. B
PubMed ID20166694
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