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Photoreaction in BLUF Receptors: Proton‐coupled Electron Transfer in the Flavin‐Gln‐Tyr System †
Author(s) -
Udvarhelyi Anikó,
Domratcheva Tatiana
Publication year - 2011
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.2010.00884.x
Subject(s) - flavin group , chemistry , flavin mononucleotide , chromophore , electron transfer , proton coupled electron transfer , flavoprotein , proton , photochemistry , relaxation (psychology) , ground state , excited state , flavin adenine dinucleotide , photoinduced electron transfer , atomic physics , cofactor , physics , psychology , social psychology , biochemistry , quantum mechanics , enzyme
Photoinduced electron transfer from tyrosine to the flavin chromophore is involved in activation of BLUF (sensor of blue light using FAD) photoreceptors. We studied the electron transfer (ET) coupled with proton‐transfer (PT) reactions, by means of XMCQDPT2//CASSCF calculations on a molecular cluster model. By defining a minimum active space in the CASSCF calculations, we could compute the entire photoreaction pathway. We find that the crossing of the locally excited and ET states is located along the flavin bond‐stretching coordinate. The ET state is stabilized by a proton transfer from the electron donor to the electron acceptor. We mapped two different PT pathways from tyrosine to flavin via the conserved glutamine. These reactions generate a tautomeric form of glutamine. Along the PT coordinates, we find geometries where the ET and the electronic ground states degenerate. At the state crossing structures, either formation of the ground state biradical intermediate or a relaxation back to the Franck–Condon minimum takes places. The computed relaxation pathways reveal that the hydrogen bonds involving glutamine in the chromophore‐binding pocket control BLUF photoefficiency.