Protein, photosensor

Time-Resolved Detection of Intermolecular Interaction of Photosensor Proteins... 

Abstract. A recently developed new method to monitor reaction kinetics of intermolecular interaction is reviewed. This method is based on the measurement of the time-dependent diffusion coefficient using the pulsed-laser-induced transient grating technique. Using this method, conformation change, transient association, and transient dissociation on reactions are successfully detected. The principle and some applications to studies on changes in the intermolecular interactions of photosensor proteins (e.g., photoactive yellow protein, phototropins, AppA) in the time domain are described. In particular, unique features of this time-dependent diffusion coefficient method are discussed. 

This photoinduced dimer finally dissociates to the original species, because the TG signal is reproducible when the repetition rate of the excitation is low enough. This leads to the conclusion that there is no covalent bond formation in the aggregated state. This was the first report showing the dimerization rate of photosensor proteins in the short-lived signaling process. Later, the origin of the photoinduced association was attributed to the exposure of the hydrophobic surface by the initial reaction [56]. 

Since PYP is one of the most well-characterized photosensors it has attracted a lot of attention from computational chemists. Robb et al. have used a QM/MM molecular dynamics strategy to examine the complete photocycle of PYP [12]. By comparing the behavior of the chromophore in vacuo with that of the chromophore within the protein they were able to determine the chemical role of the protein cavity. They found that CTI of the chromophore does not occur in vacuo, however in the protein the isomerization is facilitated by electrostatic stabilization of the chromophore s excited state with the guanidium group of Arg52 that lies just above the negatively charged phenolate of the chromophore. 

Phototaxis in Rb. sphaeroides is triggered by the effects of the photosynthetic machinery on the rate of electron transfer (9). Thus, in contrast to the situation in H. salinarum, phototaxis in Rb. sphaeroides does not involve a dedicated photosensor. The rate of electron transfer is presumably sensed by an as yet unidentified receptor, and relayed into the complex set of Che proteins in Rb. sphaeroides (Fig. 1). Thus, phototaxis responses in Rb. sphaeroides can be regarded as a form of redox taxis and are modulated by factors affecting electron transport, such as the presence or absence of oxygen (19). The Rb. sphaeroides encodes nine transmembrane chemoreceptors (MCPs) and four putative cytoplasmic MCPs, four CheA proteins, and six CheY proteins (20). A number of proteins from this Che system have been shown to be required for phototaxis in Rb. sphaeroides, showing that the signal transduction chains for phototaxis and chemotaxis converge at this level (21). A similar situation holds for phototaxis and chemotaxis in R. centenum (see later). 

Optically induced cis-trans isomerization is a key structural dynamic element for many types of photochromic switches as stilbenes and azobenzene derivatives and for photosensor proteins as bacteriorhodopsin, rhodopsin, and photoactive yellow protein. 

HeUingwerf, K.J., Key issue in the photochemistry and signaUing-state formation of photosensor proteins, /. Photochem. Photobiol. B Biol., 54, 94, 2000. 

Phytochromes are the best-characterized plant photosensors. Individual plants contain multiple functional phytochromes. Five phytochrome genes were characterized in Arabidopsis (PHYA, PHYB, PHYC, PHYD, and PHYEy and in tomato PHYA, PHYBl, PHYB2, PHYE, and PHYF)d Arabidopsis PHYA, PHYB, PHYC, and PHYE encode proteins that share 46 to 53% amino acid sequence identity, while PETYD encoded apoprotein (phyD) shares 80% amino acid sequence identity with phyB, and therefore, it is a member of the same subfamily. ... 

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