Femtosecond stimulated raman study of the photoactive flavoprotein AppA_BLUF

Femtosecond stimulated Raman Spectroscopy (FSRS) is applied to study the photocycle of a blue light using flavin (BLUF) domain photoreceptor, AppABLUF. It is shown that FSRS spectra are sensitive to the light adapted state of the protein and probe its excited state dynamics. The dominant contribution to the most sensitive excited state Raman active modes is from flavin ring modes. However, TD-DFT calculations for excited state structures indicate that reproduction and assignment of the experimentally observed spectral shift will require high level calculations on the flavin in its specific protein environment.