Couplings between peptide linkages across a 3(10)-helical hydrogen bond revealed by two-dimensional infrared spectroscopy.
Vibrational couplings between the amide modes are keenly dependent on peptide structure. Site-specific couplings can inform us of molecular conformation in detail. For example, when an amide-I mode couples to an amide-II mode that is three residues away because they are brought into proximity in the presence of an intramolecular C=O...H-N hydrogen bond, the coupling can provide direct evidence for single helical turn formation, a proposed key step in coil-helix transition. In this work, we measure 2D IR spectra of a 3(10)-helical hexapeptide, Z-Aib-l-Leu-(Aib)(2)-Gly-Aib-OtBu, and its (13)C=(18)O-Leu monolabeled and (13)C=(18)O-Leu/(15)N-Gly bis-labeled isotopomers in CDCl(3). The isotope-dependent amide-I/II cross-peaks clearly reveal the existence of vibrational coupling between the second and fourth peptide linkages that are connected through a 3(10)-helical hydrogen bond. Our results demonstrate that the combination of 2D IR and (13)C=(18)O/(15)N labeling is a useful structural method for probing local peptide conformation with residue-level specificity.
Maekawa
Hiroaki
H
Department of Chemistry, University of California at Irvine, Irvine, California 92697-2025, USA.
De Poli
Matteo
M
Toniolo
Claudio
C
Ge
Nien-Hui
NH
D000577:Amides / Q000737:chemistry; D000621:Aminoisobutyric Acids / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013055:Spectrophotometry, Infrared / Q000379:methods*
D000577:Amides; D000621:Aminoisobutyric Acids; D009842:Oligopeptides; C100049:2-aminoisobutyric acid