title: Light-induced flipping of a conserved glutamine sidechain and its orientation in the AppA BLUF domain.
abstract: The AppA BLUF domain is a blue light photoreceptor containing flavin. Conserved glutamine 63 is necessary for the photocycle of the protein, and its side chain has been proposed to flip in response to blue light illumination. Recently published crystal structures of AppA WT and the AppA mutant C20S describe contradictory conclusions regarding the orientation of the conserved glutamine 63 side chain in the dark. Here, we present evidence from NMR spectroscopy confirming light-induced flipping of the glutamine side chain to form a strong hydrogen bond between the glutamine 63 side chain carbonyl group and the tyrosine 21 side chain hydroxyl proton in the light-induced state. Our conclusions are consistent with published data from UV/vis absorbance and FTIR spectroscopy, as well as the crystal structure of AppA WT.
authors.affiliation: Department of NMR Spectroscopy, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Grinstead
authors.forename: Marcela
authors.initials: M
authors.lastname: Avila-Perez
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Hellingwerf
authors.forename: Rolf
authors.initials: R
authors.lastname: Boelens
authors.forename: Robert
authors.initials: R
authors.lastname: Kaptein
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D017124:Conserved Sequence; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry; D005420:Flavoproteins / Q000737:chemistry*; D005973:Glutamine / Q000737:chemistry; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010777:Photochemistry; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: C116785:AppA protein, Rhodobacter sphaeroides; D001426:Bacterial Proteins; D005420:Flavoproteins; D020283:Photoreceptors, Microbial; D005973:Glutamine; D005182:Flavin-Adenine Dinucleotide