Orientation of a key glutamine residue in the BLUF domain from AppA revealed by mutagenesis, spectroscopy, and quantum chemical calculations.
The flavin-adenine-dinucleotide-binding BLUF domain constitutes a new class of blue-light receptors, and the N-terminal domain of AppA is a representative of this family. A crystal structure of the BLUF domain from AppA suggested that a conserved Gln63 forms a hydrogen bond with the flavin N5 atom. Upon light excitation, this residue is proposed to undergo a approximately 180 degrees rotation that leads to a rearrangement of a hydrogen bonding network. However, crystallographic studies on the other BLUF proteins claimed an opposite orientation for the glutamine residue. In this communication, we have revealed the presence of a Gln63-to-N5 hydrogen bond in the dark state of AppA by a combined approach of mutagenesis, spectroscopy, and quantum chemical calculations. The present finding supports the view that the reorientation of the Gln63 side chain is a key event in the signaling state formation of BLUF proteins.
Unno
Masashi
M
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan. unno@cc.saga-u.ac.jp
Masuda
Shinji
S
Ono
Taka-aki
TA
Yamauchi
Seigo
S
D015226:Dinucleoside Phosphates / Q000737:chemistry*; D005973:Glutamine / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D016296:Mutagenesis; D011789:Quantum Theory; D013057:Spectrum Analysis / Q000379:methods*
D015226:Dinucleoside Phosphates; D005973:Glutamine; C012276:diadenosine pyrophosphate