Electron transfer pathways in a light, oxygen, voltage (LOV) protein devoid of the photoactive cysteine
Congratulations Dr. Mehdi D. Davari on his recent publication!
Blue-light absorption by the flavin chromophore in light, oxygen, voltage (LOV) photoreceptors triggers photochemical reactions that lead to the formation of a flavin-cysteine adduct. While it has long been assumed that adduct formation is essential for signaling, it was recently shown that LOV photoreceptor variants devoid of the photoactive cysteine can elicit a functional response and that flavin photoreduction to the neutral semiquinone is sufficient for signal transduction. Currently, the mechanistic basis of the underlying electron- (eT) and proton-transfer (pT) reactions is not well understood.
In this collaborative study, we reengineered pT into the naturally not photoreducible iLOV protein. A single amino acid substitution (Q489D) was sufficient to enable efficient photoreduction under aerobic conditions, which suggests that an eT pathway is naturally present in the protein. Employing this variant, we investigated the underlying eT and pT reactions using a combination of steady-state UV/Vis, transient absorption, electron paramagnetic resonance spectroscopy combined with site-directed mutagenesis. Our study provides strong evidence that several Tyrosine and Tryptophan residues, highly conserved in all LOV proteins, constitute the eT pathway for flavin photoreduction, suggesting that the propensity for photoreduction is evolutionary imprinted in all LOV domains, while efficient pT is needed to stabilize the neutral semiquinone radical.
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Kopka, B., Magerl, K., Savitsky, A., Davari, M.D., Röllen, K., Bocola, M., Dick, B., Schwaneberg, U., Jaeger, K.E., Krauss, U.; Electron transfer pathways in a light, oxygen, voltage (LOV) protein devoid of the photoactive cysteine; Scientific Reports 7, Article number: 13346 (2017); doi:10.1038/s41598-017-13420-1