<br/>The photocycle of the blue light using flavin (BLUF) photoreceptors involves double proton transfer upon photoexcitation. However, several question regarding its mechanism remain open. We present a study to provide insight into the double proton transfer mechanism of the Slr1694 BLUF photoreceptor. Potential energy surfaces of the ground state and excited states along the two proton transfer coordinates were computed using the complete active space self-consistent field method with an automated active space selection algorithm and multireference perturbation theory to assess the feasibility of double proton transfer on different electronic states. These computations were performed for different conformations of the active site to evaluate the impact of structural changes on proton and electron transfer. To examine the effect of the protein and solvent environment, we also performed the calculations using the electrostatic embedding. Double proton transfer was found to be energetically favorable only on the charge transfer state associated with electron transfer from Tyr8 to the flavin. The proposed mechanism is that excitation of the flavin to the locally excited state causes its polarization, inducing reorganization of the protein around the active site. This reorganized protein environment can stabilize the charge transfer state and facilitate double proton transfer on this state.

Elucidating double proton transfer mechanism in the Slr1694 BLUF photoreceptor using automated multireference calculations

2019 Spring National Meeting

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