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          Institute: MPI für medizinische Forschung     Collection: Jahbruch 2014_archival     Display Documents

ID: 681493.0, MPI für medizinische Forschung / Jahbruch 2014_archival
Photoinduced electron transfer facilitates tautomerization of the conserved signaling glutamine side chain in BLUF protein light sensors
Translation of Title:Photoinduced electron transfer facilitates tautomerization of the conserved signaling glutamine side chain in BLUF protein light sensors
Authors:Khrenova, Maria G.; Nemukhin, Alexander V.; Domratcheva, Tatiana
Date of Publication (YYYY-MM-DD):2013-02-28
Title of Journal:Journal of Physical Chemistry B
Journal Abbrev.:J. Phys. Chem. B
Issue / Number:8
Start Page:2369
End Page:2377
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:The BLUF domain (sensor of blue light using flavin adenine dinucleotide) from a bacterial photoreceptor protein AppA undergoes a cascade of chemical transformations, including hydrogen bond rearrangements around the flavin adenine dinucleotide (FAD) chromophore, in response to light illumination. These transformations are initiated by photoinduced electron and proton transfer from a tyrosine residue to the photoexcited flavin which is assisted by a glutamine residue. According to the recent studies, the proton−coupled electron transfer leads to formation of a radical−pair intermediate Tyr•···FADH• and a tautomeric EE form of glutamine in the ground electronic state. This intermediate is a precursor of the light−induced state of the BLUF photoreceptor implicated in biological signaling. In order to describe evolution of the radical pair, we computed reaction pathways on the ground state potential energy surface employing quantum−chemical calculations in the DFT PBE0/cc−pVDZ approximation for a molecular cluster mimicking the chromophore containing pocket of the AppA BLUF protein. We found a minimum−energy pathway comprised of the following consecutive reaction steps: (1) rotation of the imidic group of the EE glutamine side chain around the Cγ−Cδ bond; (2) flip of the OεH group and formation of the ZE form of the glutamine side chain; and (3) biradical recombination via coupled proton and electron transfer, leading to the ZZ form of the glutamine side chain. The potential−energy barriers for stages 1−3 do not exceed 9 kcal/mol. Energy barrier 3 describing the ZE to ZZ glutamine tautomerization is significantly smaller in the BLUF model than in isolated glutamine, since tautomerization in BLUF is facilitated by electron transfer and radical recombination. Thus, our study shows that tautomerization of the conserved glutamine is coupled to the light−induced electron transfer process in BLUF and, thus, is a viable candidate for the photoactivation mechanism which at present is very much debated
External Publication Status:published
Document Type:Article
Communicated by:wkaiser
Affiliations:MPI für medizinische Forschung/Abteilung Biomolekulare Mechanismen
MPI für medizinische Forschung/Abteilung Biomolekulare Mechanismen/Computational Photobiology
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