Abstract
Phytochromes are highly versatile photoreceptors, which occur ubiquitously in plants as well as in many light-responsive microorganisms. Here, photosynthetic cyanobacteria utilize up to three different phytochrome architectures, where only the plant-like and the single-domain cyanobacteriochromes are structurally characterized so far. Cph2 represents a third group in Synechocystis species and affects their capability of phototaxis by controlling c-di-GMP synthesis and degradation. The 2.6-Å crystal structure of its red/far-red responsive photosensory module in the Pr state reveals a tandem-GAF bidomain that lacks the figure-of-eight knot of the plant/cph1 subfamily. Its covalently attached phycocyanobilin chromophore adopts a highly tilted ZZZssa conformation with a novel set of interactions between its propionates and the GAF1 domain. The tongue-like protrusion from the GAF2 domain interacts with the GAF1-bound chromophore via its conserved PRXSF, WXE, and W(G/A)G motifs. Mutagenesis showed that the integrity of the tongue is indispensable for Pr → Pfr photoconversion and involves a swap of the motifs' tryptophans within the tongue-GAF1 interface. This "Trp switch" is supposed to be a crucial element for the photochromicity of all multidomain phytochromes.
Highlights
Phytochromes are red/far-red photoreceptors using a bilin chromophore
PCC 6803 (SynCph[1] (7)) as well as fungal and eubacterial bacteriophytochromes. These phytochromes use a three-domain PAS-GAFPHY (PAS, period/ARNT/single-minded; PHY, phytochrome) photosensory module, where an unusual figure-of-eight knot is formed by the N terminus of the PAS domain and a loop protruding from the chromophore-binding GAF domain (Fig. 1A)
The interactions between the tongue region of GAF2 and the bilin-binding site of GAF1 are conserved, implying a universal route for signal transduction in Group I and II phytochromes that involves a toggling of conserved Trp motifs within the tongue/GAF1 interface
Summary
Phytochromes are red/far-red photoreceptors using a bilin chromophore. Results: Compared with Cph[1], the Cph[2] bilin-binding site differs around the propionates, but utilizes an otherwise conserved tongue for sealing the chromophore from solvent. PCC 6803 (SynCph[1] (7)) as well as fungal and eubacterial bacteriophytochromes These phytochromes use a three-domain PAS-GAFPHY (PAS, period/ARNT/single-minded; PHY, phytochrome) photosensory module, where an unusual figure-of-eight knot is formed by the N terminus of the PAS domain and a loop protruding from the chromophore-binding GAF domain (Fig. 1A). The complex architecture of SynCph[2] (Fig. 1A) harbors at its N terminus the red/far-red sensitive tandemGAF module (SynCph2(1–2) (10)) that precedes a GGDEF*EAL effector module, and CBCR and catalytically active GGDEF domains This C-terminal CBCR-GGDEF module is capable of switching between blue and green light sensitive states and controls the catalytic activity of the GGDEF domain, thereby inhibiting motility by increasing c-di-GMP levels (17). The interactions between the tongue region of GAF2 and the bilin-binding site of GAF1 are conserved, implying a universal route for signal transduction in Group I and II phytochromes that involves a toggling of conserved Trp motifs within the tongue/GAF1 interface
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
