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Light-induced structural changes for the signaling state formation are studied using the light-induced Fourier transform infrared (FTIR) difference spectroscopy of both the full-length YcgF protein (YcgF-Full) and its BLUF domain (YcgF-BLUF). YcgF-Full and YcgF-BLUF show identical UV-visible absorption redshifts for FAD upon illumination, and the possibility of full-length-specific protein bands being responsible for the C-terminal EAL domain structural changes in the signaling state due to light excitation of the N-terminal BLUF domain is discussed.

The three-dimensional dark state structure of the flavin-binding BLUF (blue light sensing using FAD) domain of AppA from Rhodobacter sphaeroides is described. The domain represents a new class of flavin-binding proteins involved in light sensing, its structure to that of other related proteins is compared and the implications of the structure for signaling mechanisms is discussed.

Research indicates that in Rhodovulum sulfidophilum cytochrome c(sub)2 is not the dominant electron donor to reaction center as a soluble cytochrome, c-549, donates electron to the reaction center-bound triheme cytochrome. This process is different from those of other purple bacteria.

PapB, which contains a BLUF domain, has controlled the biofilm formation of the purple photosynthetic bacterium Rhodopseudomonas palustris and purified PapB has undergone BLUF-type photocycle and light-excited PapB has increased the phosphodiesterase activity of the EAL domain protein, PapA. The studies have shown that Rhodopseudomonas palustris has controlled biofilm formation via a blue light-dependent modulation of its cyclic dimeric GMP level by the BLUF domain protein, PapB.

The time-resolved transient grating method was used to study the spectrally silent photoreaction of a blue light sensor protein YcgF, composed of the N-terminal BLUF domain and the C-terminal EAL domain. The temperature sensitivity of the photoreaction of YcgF indicated the possible contribution of YcgF protein for biological function as a temperature sensor as well as behaving as a light sensor.

The pulsed laser-induced transient grating (TG) method is used for investigating the photochemical reaction dynamics of YcgF, a BLUF protein. The photochemical reaction of YcgF is described and it is shown that the diffusive-sensitive conformational change might be an essential process for the creation of the signaling state.

A study provides evidence that blue light photoreceptor Slr1694 shows three different tertiary structures involving the sole Trp residue and the fifth [beta]-strand of their [beta]-sheet. Spectral and mutational evidence indicate that these differences are related to flavin excitation upon blue light absorption and, hence, to signaling.

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.

Light-dependent changes in the active site of an AppA BLUF domain by Raman spectroscopy are characterized. The structural alterations are proposed to be responsible for the transmission of the light signal in the BLUF domain.

An in vitro reconstitution method is developed by which a fully functional sensor of blue light using flavin adenine dinucleotide (BLUF) domain was reconstituted from free flavin adenine dinucleotide (FAD) and an apoprotein for the BLUF domain of AppA. The results obtained showed that relatively large structural changes occur in the protein backbone of the BLUF domain of AppA upon illumination.

Slrl1694 in Synechocystis sp. PCC6803 is a family of blue-light photoreceptors based on flavin adenine dinucleotide (FAD) called BLUF proteins, which include AppA from Rhodabacter sphaeroides and PAC from Euglena gracilis. It is found that the illumination at the medium-low temperature or under dehydrated conditions induces a photoinduced state, which is considerably different from the signaling light state induced by illuminating the hydrated Slrl1694 at 15 degree Celsius.

Synechocystis sp. PCC6803 Slr1694 shows almost identical light-induced changes in the UV-visible absorption spectrum with AppA but much faster back reaction rate from the light-excited state to the dark state indicates that Slr1694 is a blue-light receptor based on BLUF. Information for the understanding of the blue-light perception mechanism of the BLUF photoreceptor is presented.

Research has been conducted on flavoprotein Appa, a blue-light photoreceptor which is photosynthesis gene expression antirepressor. Results suggest that photochemical excitation of flavin produces a hydrogen bond between a flavin and Tyr 21.

S1r1694 in Synechocystis sp. PCC6803 is a family of blue-light photoreceptors based on flavin adenine dinucleotide (FAD) called BLUF (sensor of blue light using FAD) proteins, which include AppA from Rhodobacter sphaeroides and PAC from Euglena gracilis. Illumination of dark-state S1r1694 at 15 °C reversibly induced a signaling light state characterized by the red shift in the UV-visible spectrum and by the light-induced Fourier transform infrared (FTIR) difference spectrum for structural changes of a bound flavin and apo protein. Illumination at the medium-low temperature (-35 °C) led to the red shift in the UV-visible spectrum despite some small difference in the light-induced changes. In contrast, the -35 °C illumination resulted in a completely different light-induced FTIR spectrum, in which almost all of the bands were suppressed with the exception of the bands for the change of C4=O bonding of the FAD isoalloxazine ring. The C4=O bands were induced at -35 °C with almost the same intensity, but the band frequency for the light state was upshifted by 6 cm-1. The changes in frequency of the light- state C4=O band and in amplitude of other bands showed the same temperature dependence with a half- change temperature at approximately -20 °C. It was indicated that the light-induced structural changes of apo protein and FAD were inhibited at low temperature with the exception of the change in hydrogen bonding to the C4=O group. The light-induced formation of the FTIR bands was similarly inhibited by sample dehydration. We discussed the possibility that this constrained light state is a trapped intermediate state in the photocycle of Slr1694. [ABSTRACT FROM AUTHOR]

Describes the mutational analyses of the photosynthetic reaction center-bound triheme cytochrome subunit. Physiological role of proteins for photosynthetic electron transfer; Conformation of chromosomal insertion; Effects of residual soluble cytochromes on closed chromatophores.

The article characterizes the effects of Gln63 → Leu (Q63L) mutation, which removes a putative hydrogen bond between the flavin ring and the Gln63 side chain, on Raman and ultraviolet-visible absorption spectra in the BLUF domain of AppA. The results demonstrate the absence of a hydrogen bond between Gln63 and the flavin C4++O in the dark state AppA in solution. The observed spectral changes are theoretically evaluated using quantum chemical calculations based on density functional theory.

Femtosecond time-resolved absorption measurements were carried out for the dark and signaling states of a BLUF (Blue Light Using FAD) protein, PixD, from the cyanobacterium Synechocystis . When the dark state was excited, FAD semiquinone radical (FADH • ) was produced from the S 1 state, and FADH • led to the signaling state. On the other hand, photoexcitation of the signaling state generated FADH • and FAD anion radical (FAD •- ), and they decayed back to the original signaling state. In both cases, FADH • was formed and decayed with a proton-coupled electron transfer (PCET) via the hydrogen-bond network that involves FAD, Gln50, and Tyr8, and hence the kinetics of FADH • directly reflects the hydrogen-bond structure in the FAD-binding sites. It was found that the formation rate of FADH • was significantly different between the dark and signaling states, whereas the decay rate was the same. This indicates that the hydrogen-bond network of FAD-Gln50-Tyr8 in the dark and signaling states is initially different but it becomes indistinguishable after FADH • is formed, implying that the FAD-Gln50-Tyr8 hydrogen-bond network is rearranged during the PCET to generate FADH • . The present results best agree with the model in which the Gln tautomerizes without rotation in the signaling-state formation.

We developed a novel technique for manipulating the activity of transcription factors with blue light (termed "PICCORO") using the bacterial BLUF-type photoreceptor protein PixD. The chimeric dominant-negative T-box transcription factor No Tail formed heterologous complexes with a PixD decamer in a light-dependent manner, and these complexes affected transcription repressor activity. When applied to zebrafish embryos, PICCORO permitted regulation of the activity of the mutant No Tail in response to 472-nm light provided by a light-emitting diode.