Computational modeling reveals the mechanism of fluorescent state recovery in the reversibly photoswitchable protein Dreiklang

B. L. Grigorenko, I. Polyakov, A. I. Krylov, and A. V. Nemukhin
J. Phys. Chem. B  123, 8901 – 8909 (2019)

The unique properties of the photoswitchable protein Dreiklang are attributed to a reversible hydration/dehydration reaction at the imidazolinone ring of the chromophore. Recovery of the fluorescent state, which is associated with a chemical reaction of chromophore dehydration, is an important part of the photocycle of this protein. Here we characterize the fluorescent (ON) and non-fluorescent (OFF) states of Dreiklang and simulate the thermal recovery reaction OFF -> ON using computational approaches. By using molecular modeling methods including the quantum mechanics/molecular mechanics (QM/MM) technique, we characterize the structures and spectra of the ON- and OFF-states. The results are consistent with relevant experimental data. The computed reaction profile explains the observed recovery reaction and clarifies the mechanism of chemical transformations in the chromophore-containing pocket in Dreiklang.

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