Relationship between rate of photoinduced electron transfer and hydrogen bonding chain of tyrosine-glutamine-flavin in flavin photoreceptors: Global analyses among four TePixDs and three AppAs

Abstract

Relationship was studied between rates of photoinduced electron transfer (PET) from individual aromatic amino acid and hydrogen bonding (H-bond) chain of Tyr-Gln-isoalloxazine (Iso) among seven flavin photoreceptors (FPR); four TePixDs [wild type (WT), Q50N (amino Gln50 was replaced by Asn), Q50A (Gln50 replaced by Ala), and Y8F (Tyr8 replaced by Phe)] and three AppAs [WT, W92F (Trp92 replaced by Phe), and Y9F (Tyr9 replaced by Phe)]. The PET rates were obtained from the reported fluorescence dynamics of the seven FPRs with atomic coordinates determined by molecular dynamic simulations (MDS) and Kakitani and Mataga (KM) electron transfer theory. In TePixD isoforms, the fastest PET rate was obtained to be of 4.0 × 10−2 ps−1 from Tyr8 to Iso* in WT, while the rates were 8.7 × 10−3 ps−1 from Trp91 in Q50N, 7.0 × 10−2 ps−1 from Trp91 in Q50A and 1.1 × 10−3 ps−1 from Trp91 in Y8F. Similarly, the fastest PET rates in AppAs were 4.4 × 10−3 and 1.1 × 10−3 ps−1 from Tyr9 to Iso* in both WT and W92F. Formations of H-bonds between Tyr and Iso were examined by MDS snapshots. Tyr8-Gln50-Iso H-bond chain in TePixD was found only in WT among the four isoforms, whereas Tyr9-Gln51-Iso H-bond chain in AppA was found in both WT and W92F. It was found that the PET rates from Tyr8 in TePixD and Tyr9 in AppA were fastest when Tyr, Gln and Iso form H-bond chains. The rates from the Tyrs were much faster than one from Tyr with similar donor-acceptor distance in non-FPR flavoprotein of FMN binding protein. The reasons for it were discussed with PET parameters contained in KM theory.