Structure of a bacterial BLUF photoreceptor: Insights into blue light-mediated signal transduction

Jung, Astrid; Domratcheva, Tatiana; Tarutina, M. G.; Wu, Qiong; Ko, Wen-huang; Shoeman, Robert L.; Gomelsky, Mark; Gardner, Kevin H.; Schlichting, Ilme

doi:10.1073/pnas.0500722102

Cited by 166 publications

(292 citation statements)

References 35 publications

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“…4). Finally, the short BLUF protein, BlrB from R. sphaeroides, adapts a very similar [AB] dimer form in its crystal structure (Protein Data Bank ID code 2BYC) (23). Collectively, these results suggest that PixD exists in solution as a stable [AB] dimer that oligomerizes in the dark with the help of PixE to form a stacked set of pentameric rings (Fig.…”

Section: Discussionmentioning

confidence: 65%

PixE promotes dark oligomerization of the BLUF photoreceptor PixD

Yuan

Bauer

2008

Proc. Natl. Acad. Sci. U.S.A.

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Cyanobacteria perceive and move (phototax) in response to blue light. In this study, we demonstrate that the PixD blue light-sensing using FAD (BLUF) photoreceptor that governs this response undergoes changes in oligomerization state upon illumination. Under dark conditions we observed that PixD forms a large molecular weight complex with another protein called PixE. Stoicheometric analyses, coupled with sedimentation equilibrium and size exclusion chromatography, demonstrates that PixE drives aggregation of PixD dimers into a stable PixD10-PixE5 complex under dark conditions. Illumination of a flavin chromophore in PixD destabilizes the PixD10-PixE5 complex into monomers of PixE and dimers of PixD. A crystallographic structure of PixD, coupled with Gibbs free energy calculation between interacting faces of PixD, lends to a model in which a light induces a conformational change in a critical PixD-interfacing loop that results in destabilization of the PixD10-PixE5 complex.flavin chromophore ͉ phototaxis ͉ synechocystis

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Section: Discussionmentioning

confidence: 65%

PixE promotes dark oligomerization of the BLUF photoreceptor PixD

Yuan

Bauer

2008

Proc. Natl. Acad. Sci. U.S.A.

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“…Early studies suggested that an increased -stacking between Tyr and FAD, or deprotonation of FAD, would induce signaling-state formation (15,16). Jung et al (13) proposed that in the BlrB BLUF domain, proton transfer (PT) takes place from an arginine (Arg) residue to the O2 atom of the isoalloxazine ring upon blue-light absorption, triggered by the increased basicity of O2 upon promotion of FAD to the singlet excited state. Masuda et al (17) interpreted their results from Fourier transform infrared (FTIR) spectroscopy by a hydrogen-bond rearrangement around the FAD chromophore upon signaling-state formation.…”

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confidence: 99%

“…Recently, crystal and solution structures of several BLUF domains were obtained (11)(12)(13)(14). The BLUF domain shows a ferredoxin-like fold consisting of a five-stranded ␤-sheet with two ␣-helices packed on one side of the sheet, with the noncovalently bound isoalloxazine ring of flavin adenine dinucleotide (FAD) positioned between the two ␣-helices.…”

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confidence: 99%

Hydrogen-bond switching through a radical pair mechanism in a flavin-binding photoreceptor

Gauden

Stokkum²,

Key³

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

217

435

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BLUF (blue light sensing using FAD) domains constitute a recently discovered class of photoreceptor proteins found in bacteria and eukaryotic algae, where they control a range of physiological responses including photosynthesis gene expression, photophobia, and negative phototaxis. Other than in well known photoreceptors such as the rhodopsins and phytochromes, BLUF domains are sensitive to light through an oxidized flavin rather than an isomerizable cofactor. To understand the physicochemical basis of BLUF domain photoactivation, we have applied femtosecond transient absorption spectroscopy to the Slr1694 BLUF domain of Synechocystis PCC6803. We show that photoactivation of BLUF domains proceeds by means of a radical-pair mechanism, driven by electron and proton transfer from the protein to the flavin, resulting in the transient formation of anionic and neutral flavin radical species that finally result in the long-lived signaling state on a 100-ps timescale. A pronounced deuteration effect is observed on the lifetimes of the intermediate radical species, indicating that proton movements underlie their molecular transformations. We propose a photoactivation mechanism that involves a successive rupture of hydrogen bonds between a conserved tyrosine and glutamine by light-induced electron transfer from tyrosine to flavin and between the glutamine and flavin by subsequent protonation at flavin N5. These events allow a reorientation of the conserved glutamine, resulting in a switching of the hydrogen-bond network connecting the chromophore to the protein, followed by radicalpair recombination, which locks the glutamine in place. It is suggested that the redox potential of flavin generally defines the light sensitivity of flavin-binding photoreceptors.flavoprotein ͉ light sensing ͉ photochemistry ͉ reaction mechanism ͉ spectroscopy

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“…Especially members of the BLUF 1 (blue light photoreceptors using FAD) family (1)(2)(3) show an especially intriguing light-induced proton network rearrangement resulting in a 10-15 nm red-shifted spectrum of the signaling state. The BLUF domain shows a ferredoxin-like fold consisting of a five-stranded β-sheet with two R-helices packed on one side of the sheet, with the isoalloxazine ring of flavin adenine dinucleotide (FAD) positioned between the two R-helices (4)(5)(6)(7)(8)(9)(10)(11)(12). FAD is noncovalently bound to the protein through a number of hydrogen bonds and hydrophobic interactions.…”

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confidence: 99%

“…Another aspect in the study of BLUF photoreceptors is their rather large variety in their transient behavior. Despite their high sequence homology the signaling state lifetime of BLUF domains varies from Slr1694, BlrB (5), and Thermosynechococcus TePixD (34) with around 10 s to AppA (35) and YcgF (36) with 50-100-fold slower decay times.…”

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confidence: 99%

The Role of Key Amino Acids in the Photoactivation Pathway of the Synechocystis Slr1694 BLUF Domain

et al. 2009

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BLUF (blue light sensing using FAD) domains belong to a novel group of blue light sensing receptor proteins found in microorganisms. We have assessed the role of specific aromatic and polar residues in the Synechocystis Slr1694 BLUF protein by investigating site-directed mutants with substitutions Y8W, W91F, and S28A. The W91F and S28A mutants formed the red-shifted signaling state upon blue light illumination, whereas in the Y8W mutant, signaling state formation was abolished. The W91F mutant shows photoactivation dynamics that involve the successive formation of FAD anionic and neutral semiquinone radicals on a picosecond time scale, followed by radical pair recombination to result in the long-lived signaling state in less than 100 ps. The photoactivation dynamics and quantum yield of signaling state formation were essentially identical to those of wild type, which indicates that only one significant light-driven electron transfer pathway is available in Slr1694, involving electron transfer from Y8 to FAD without notable contribution of W91. In the S28A mutant, the photoactivation dynamics and quantum yield of signaling state formation as well as dark recovery were essentially the same as in wild type. Thus, S28 does not play an essential role in the initial hydrogen bond switching reaction in Slr1694 beyond an influence on the absorption spectrum. In the Y8W mutant, two deactivation branches upon excitation were identified: the first involves a neutral semiquinone FADH • that was formed in ∼1 ps and recombines in 10 ps and is tentatively assigned to a FADH • -W8 • radical pair. The second deactivation branch forms FADH • in 8 ps and evolves to FAD •-in 200 ps, which recombines to the ground state in about 4 ns. In the latter branch, W8 is tentatively assigned as the FAD redox partner as well. Overall, the results are consistent with a photoactivation mechanism for BLUF domains where signaling state formation proceeds via light-driven electron and proton transfer from Y8 to FAD, followed by a hydrogen bond rearrangement and radical pair recombination.Blue light photoreceptors using flavin cofactors have been the focus of recent research because of their novel mechanisms of photoactivation in contrast to "classical" photoreceptors like phytochromes and rhodopsins. Especially members of the BLUF 1 (blue light photoreceptors using FAD) family (1-3) show an especially intriguing light-induced proton network rearrangement resulting in a 10-15 nm red-shifted spectrum of the signaling state. The BLUF domain shows a ferredoxin-like fold consisting of a five-stranded β-sheet with two R-helices packed on one side of the sheet, with the isoalloxazine ring of flavin adenine dinucleotide (FAD) positioned between the two R-helices (4-12). FAD is noncovalently bound to the protein through a number of hydrogen bonds and hydrophobic interactions. Figure 1 shows the three-dimensional structure of the Synechocystis Slr1694 BLUF domain (also known as PixD) in its proposed dark and light states, with the FAD binding pock...

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Structure of a bacterial BLUF photoreceptor: Insights into blue light-mediated signal transduction

Cited by 166 publications

References 35 publications

PixE promotes dark oligomerization of the BLUF photoreceptor PixD

PixE promotes dark oligomerization of the BLUF photoreceptor PixD

Hydrogen-bond switching through a radical pair mechanism in a flavin-binding photoreceptor

The Role of Key Amino Acids in the Photoactivation Pathway of the Synechocystis Slr1694 BLUF Domain

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