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PDBsum entry 2byc
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Signaling protein
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PDB id
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2byc
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References listed in PDB file
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Key reference
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Title
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Structure of a bacterial bluf photoreceptor: insights into blue light-Mediated signal transduction.
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Authors
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A.Jung,
T.Domratcheva,
M.Tarutina,
Q.Wu,
W.H.Ko,
R.L.Shoeman,
M.Gomelsky,
K.H.Gardner,
I.Schlichting.
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Ref.
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Proc Natl Acad Sci U S A, 2005,
102,
12350-12355.
[DOI no: ]
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PubMed id
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Abstract
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Light is an essential environmental factor, and many species have evolved the
capability to respond to it. Blue light is perceived through three
flavin-containing photoreceptor families: cryptochromes, light-oxygen-voltage,
and BLUF (sensor of blue light using flavin adenine dinucleotide, FAD) domain
proteins. BLUF domains are present in various proteins from Bacteria and lower
Eukarya. They are fully modular and can relay signals to structurally and
functionally diverse output units, most of which are implicated in nucleotide
metabolism. We present the high resolution crystal structure of the dark resting
state of BlrB, a short BLUF domain-containing protein from Rhodobacter
sphaeroides. The structure reveals a previously uncharacterized FAD-binding
fold. Along with other lines of evidence, it suggests mechanistic aspects for
the photocycle that is characterized by a red-shifted absorbance of the flavin.
The isoalloxazine ring of FAD binds in a cleft between two helices, whereas the
adenine ring points into the solvent. We propose that the adenine ring serves as
a hook mediating the interaction with its effector/output domain. The structure
suggests a unique photochemical signaling switch in which the absorption of
light induces a structural change in the rim surrounding the hook, thereby
changing the protein interface between BLUF and the output domain.
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Figure 1.
Fig. 1. Spectroscopic characterization of BlrB dark and
signaling active states. (A) UV-visible absorption spectra of
dark state (black line) and signaling state (red line) of BlrB
recorded at 4°C. (B) 1H NMR spectra for the methyl regions
of BlrB recorded under dark, signaling (lit), and
postillumination dark states.
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Figure 2.
Fig. 2. Structure and active site of BlrB. (A) The
asymmetric unit of BlrB crystals contains two BlrB molecules
with ferredoxin-like topology (apoproteins in gray and flavin
cofactors in green). Secondary structure elements are assigned
in molecule A (Left). (B) The flavin-binding pocket, shown in
stereoview, is made up by the highest conserved residues of the
BLUF domain. They position the cofactor by mostly hydrophobic
interactions around the dimethylbenzene moiety and by hydrogen
bonds to heteroatoms of the light absorbing ring system and the
ribityl chain. Compared to most residues building up the
cofactor pocket, the side chain of Arg-32 is less well defined.
There is only a clear interaction with the O4' and O2 atoms of
the flavin in molecule A. Hydrogen bonds are indicated by dotted
lines, and distances are given in angstroms.
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