Orientation of a key glutamine residue in the BLUF domain from AppA revealed mutagenesis, spectroscopy and quantum chemical calculations

Reported crystal structures of Tll0078 and BlrB showed that the glutamine residue arranges in a manner that corresponds to the signaling state structure of AppA to form a hydrogen bond with the C4=O oxygen in the dark state. The effects of Gln63->Leu (Q63L) mutation are characterized, which removes a putative hydrogen bond between the flavin ring and the Gln63 side chain, on Raman and UV-visible absorption spectra in the blue light using flavin-adenine-dinucleotide (BLUF) domain of AppA.