Bacterial Photoreceptor with Similarity to Photoactive Yellow Protein and Plant Phytochromes

Abstract

A phytochrome-like protein called Ppr was discovered in the purple photosynthetic bacterium Rhodospirillum centenum. Ppr has a photoactive yellow protein (PYP) amino-terminal domain, a central domain with similarity to phytochrome, and a carboxyl-terminal histidine kinase domain. Reconstitution experiments demonstrate that Ppr covalently attaches the blue light-absorbing chromophore p-hydroxycinnamic acid and that it has a photocycle that is spectrally similar to, but kinetically slower than, that of PYP. Ppr also regulates chalcone synthase gene expression in response to blue light with autophosphorylation inhibited in vitro by blue light. Phylogenetic analysis demonstrates that R. centenum Ppr may be ancestral to cyanobacterial and plant phytochromes.

Crystal structure of a photoactive yellow protein from a sensor histidine kinase: Conformational variability and signal transduction

“…1B. Ppr-PYP maintains the conserved structural elements of PYPs (25,40) with high conservation in those residues forming its two hydrophobic cores and the chromophore binding pocket (20,25,40) and low homology in the two-helix N-terminal cap, which has been identified as a region of enhanced flexibility in an E-PYP photostationary state (21). All PYPs contain residues Cys-69, required for chromophore attachment, and Arg-52, which acts as a gate to the chromophore binding pocket.…”

“…From a plasmid encoding full-length Ppr (25), PCR amplification was performed by using N-and C-terminal primers encoding residues 1-129. The PCR product was ligated into the TOPO TrcHis vector (Invitrogen) to generate a construct of Ppr-PYP with an N-terminal hexahistidine tag and enterokinase cut site.…”

“…In Ppr, absorption of blue light by its PYP domain results in inhibition of its histidine kinase activity. A R. centenum Ppr knockout showed no defects in phototaxis but had lower levels of expression of chalcone synthase, an enzyme involved in photoprotection through flavonoid biosynthesis (25). Although the PYP domain of Ppr (Ppr-PYP) is 45% identical in sequence to E-PYP and has similar or identical residues to all those suggested to be critical to absorption spectra and photocycle dynamics in E-PYP (26,27), Ppr-PYP has a considerably slower photocycle than E-PYP (25).…”

“…A R. centenum Ppr knockout showed no defects in phototaxis but had lower levels of expression of chalcone synthase, an enzyme involved in photoprotection through flavonoid biosynthesis (25). Although the PYP domain of Ppr (Ppr-PYP) is 45% identical in sequence to E-PYP and has similar or identical residues to all those suggested to be critical to absorption spectra and photocycle dynamics in E-PYP (26,27), Ppr-PYP has a considerably slower photocycle than E-PYP (25). Furthermore, as Ppr-PYP controls the activity of a histidine kinase, its study affords not only the opportunity to understand the signaling mechanism of PYPs, but of the entire class of PAS-domain-regulated sensor histidine kinases, which are ubiquitous in bacteria (28).…”

“…The identification of the novel photoreceptor Ppr from Rhodospirillum centenum, which has a PYP domain linked to bacteriophytochrome and histidine kinase domains (25), may enable us to understand how PYPs are able to generate and transmit biological signals to effector domains and how such signaling activity is associated with photocycle dynamics. In Ppr, absorption of blue light by its PYP domain results in inhibition of its histidine kinase activity.…”