Journal
CHEMPHYSCHEM
Volume 15, Issue 15, Pages 3282-3290Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201402374
Keywords
ab initio calculations; charge transfer; conformation analysis; protein folding; UV/Vis spectroscopy
Funding
- European Research Council [291198]
- National Institute of Health [GM-59230]
- National Science Foundation [CHE-1058791]
- Direct For Mathematical & Physical Scien [1361516] Funding Source: National Science Foundation
- Division Of Chemistry [1361516] Funding Source: National Science Foundation
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The ability of nonlinear electronic spectroscopy to track folding/unfolding processes of proteins in solution by monitoring aromatic interactions is investigated by first-principles simulations of two-dimensional (2D) electronic spectra of a model peptide. A dominant reaction pathway approach is employed to determine the unfolding pathway of a tetrapeptide, which connects the initial folded configuration with stacked aromatic side chains and the final unfolded state with distant noninteracting aromatic residues. The p-stacking and excitonic coupling effects are included through ab initio simulations based on multiconfigurational methods within a hybrid quantum mechanics/molecular mechanics scheme. It is shown that linear absorption spectroscopy in the ultraviolet (UV) region is unable to resolve the unstacking dynamics characterized by the three-step process: T-shaped -> twisted offset stacking -> unstacking. Conversely, pump-probe spectroscopy can be used to resolve aromatic interactions by probing in the visible region, the excited-state absorptions (ESAs) that involve charge-transfer states. 2DUV spectroscopy offers the highest sensitivity to the unfolding process, by providing the disentanglement of ESA signals belonging to different aromatic chromophores and high correlation between the conformational dynamics and the quartic splitting.
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