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Enhanced Sensitivity to Local Dynamics in Peptides by Use of Temperature‐Jump IR Spectroscopy and Isotope Labeling
Author(s) -
Scheerer David,
Chi Heng,
McElheny Dan,
Keiderling Timothy A.,
Hauser Karin
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201904497
Subject(s) - isotope , chemistry , spectroscopy , kinetic isotope effect , relaxation (psychology) , rotational–vibrational coupling , chemical physics , molecular vibration , molecule , infrared spectroscopy , temperature jump , fourier transform infrared spectroscopy , sensitivity (control systems) , analytical chemistry (journal) , deuterium , atomic physics , organic chemistry , physics , optics , psychology , social psychology , quantum mechanics , electronic engineering , engineering
Site‐specific isotopic labeling of molecules is a widely used approach in IR spectroscopy to resolve local contributions to vibrational modes. The induced frequency shift of the corresponding IR band depends on the substituted masses, as well as on hydrogen bonding and vibrational coupling. The impact of these different factors was analyzed with a designed three‐stranded β‐sheet peptide and by use of selected 13 C isotope substitutions at multiple positions in the peptide backbone. Single‐strand labels give rise to isotopically shifted bands at different frequencies, depending on the specific sites; this demonstrates sensitivity to the local environment. Cross‐strand double‐ and triple‐labeled peptides exhibited two resolved bands that could be uniquely assigned to specific residues, the equilibrium IR spectra of which indicated only weak local‐mode coupling. Temperature‐jump IR laser spectroscopy was applied to monitor structural dynamics and revealed an impressive enhancement of the isotope sensitivity to both local positions and coupling between them, relative to that of equilibrium FTIR spectroscopy. Site‐specific relaxation rates were altered upon the introduction of additional cross‐strand isotopes. Likewise, the rates for the global β‐sheet dynamics were affected in a manner dependent on the distinct relaxation behavior of the labeled oscillator. This study reveals that isotope labels provide not only local structural probes, but rather sense the dynamic complexity of the molecular environment.