Flavoproteins are important blue light sensors in photobiology and play a key role in optogenetics. The characterization of their excited state structure and dynamics is thus an important objective. Here, we present a detailed study of excited state vibrational spectra of flavin mononucleotide (FMN), in solution and bound to the LOV-2 (Light-Oxygen-Voltage) domain of Avena sativa phototropin. Vibrational frequencies are determined for the optically excited singlet state and the reactive triplet state, through resonant ultrafast femtosecond stimulated Raman spectroscopy (FSRS). To assign the observed spectra, vibrational frequencies of the excited states are calculated using density functional theory, and both measurement and theory are applied to four different isotopologues of FMN. Excited state mode assignments are refined in both states, and their sensitivity to deuteration and protein environment are investigated. We show that resonant FSRS provides a useful tool for characterizing photoactive flavoproteins and is able to highlight chromophore localized modes and to record hydrogen/deuterium exchange.
Bibliographical noteFunding Information:
This study was supported by the National Science Foundation (NSF) (MCB-1817837 to P.J.T., MCB-1750637 to J.B.F.) and the EPSRC (EP/N033647/1 to S.R.M.). J.N.I. was supported by a National Institutes of Health Chemistry-Biology Interface Training Grant (T32GM092714). A.L. acknowledges funding from EFOP-3.6.2-16-2017-00005. J.B.F. acknowledges the Research Corporation for Science Advancement for a Cottrell Scholar Award. The calculations presented in this paper were carried out on the High Performance Computing Cluster supported by the Research and Specialist Computing Support service at the University of East Anglia.
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, U.S. Gov't, Non-P.H.S.
- Research Support, Non-U.S. Gov't