On the Collective Nature of Phytochrome Photoactivation

Chemical Physics Letters

Chang

et al. 2012

Femtosecond photodynamics of the reverse (15EPfr→15ZPr) reaction of the red/far-red phytochrome Cph1 from Synechocystis were resolved with visible broadband transient absorption spectroscopy. Multi-phasic dynamics were resolved and separated via global target analysis into a fast-decaying (260 fs) excited-state population that bifurcates to generate the isomerized Lumi-F primary photoproduct and a non-isomerizing vibrationally excited ground state that relaxes back into the 15EPfr ground state on a 2.8-ps time scale. Relaxation on a 1-ms timescale results in the loss of red absorbing region, but not blue region, of Lumi-F, which indicates that formation of 15ZPr occurs on slower timescales.

Section: Discussionsupporting

confidence: 79%

Ultrafast E to Z photoisomerization dynamics of the Cph1 phytochrome

Kim

Chemical Physics Letters

Chang

et al. 2012

“…NMR spectral analyses of the attached bilin chromophore are also consistent with this interpretation. NpF2164g3 is similar to the red/far-red phytochrome Cph1, which also has a more ordered chromophore-binding pocket in the photoproduct state; 37 however, NpF2164g3 is much less ordered than phytochromes in both photostates. NpF2164g3 also provides an interesting counterpoint to blue light sensors such as phototropins and photoactive yellow protein (PYP), in which light excitation leads to loss of ordered structure.…”

Section: Introductionmentioning

confidence: 98%

Photoconversion changes bilin chromophore conjugation and protein secondary structure in the violet/orange cyanobacteriochrome NpF2163g3

Lim

Photochem Photobiol Sci

Martin

et al. 2014

Cyanobacteriochromes (CBCRs) are cyanobacterial photoreceptors distantly related to phytochromes. All CBCRs examined to date utilize a conserved Cys residue to form a covalent thioether linkage to the bilin chromophore. In the insert-Cys CBCR subfamily, a second conserved Cys can covalently link to the bilin C10 methine bridge, allowing detection of near-UV to blue light. The best understood insert-Cys CBCR is the violet/orange CBCR NpF2164g3 from Nostoc punctiforme, which has a stable second linkage in the violet-absorbing dark state. Photoconversion of NpF2164g3 leads to elimination of the second linkage and formation of an orange-absorbing photoproduct. We recently reported NMR chemical shift assignments for the orange-absorbing photoproduct state of NpF2164g3. We here present equivalent information for its violet-absorbing dark state. In both photostates, NpF2164g3 is monomeric in solution and regions containing the two conserved Cys residues essential for photoconversion are structurally disordered. In contrast to blue light receptors such as phototropin, NpF2164g3 is less structurally ordered in the dark state than in the photoproduct. The insert-Cys insertion loop and C-terminal helix exhibit light-dependent structural changes. Moreover, a motif containing an Asp residue also found in other CBCRs and in phytochromes adopts a random-coil structure in the dark state but a stable α-helix structure in the photoproduct. NMR analysis of the chromophore is consistent with a less ordered dark state, with A-ring resonances only resolved in the photoproduct. The C10 atom of the bilin chromophore exhibits a drastic change in chemical shift upon photoconversion, changing from 34.5 ppm (methylene) in the dark state to 115 ppm (methine) in the light-activated state. Our results provide structural insight into the two-Cys photocycle of NpF2164g3 and the structurally diverse mechanisms used for light perception by the larger phytochrome superfamily.

“…The first was the cyanobacterial phytochrome Cph1 from Synechocystis sp. PCC 6803, a well‐characterized model protein for understanding phytochrome structure and function (Hughes et al ., ; Yeh et al ., ; Borucki et al ., ; Fischer & Lagarias, ; Fischer et al ., ; Strauss et al ., ; Hahn et al ., ; Rohmer et al ., ; Essen et al ., ; Rockwell et al ., ; Song et al ., ,b; Kim et al ., , , ,b). Cph1 exhibits considerable heterogeneity.…”

Section: Resultsmentioning

confidence: 99%

The phycocyanobilin chromophore of streptophyte algal phytochromes is synthesized by HY2

Martin

et al. 2017

New Phytologist

Summary Land plant phytochromes perceive red and far-red light to control growth and development, using the linear tetrapyrrole (bilin) chromophore phytochromobilin (PΦB). Phytochromes from streptophyte algae, sister species to land plants, instead use phycocyanobilin (PCB). PCB and PΦB are synthesized by different ferredoxin-dependent bilin reductases (FDBRs): PΦB is synthesized by HY2, whereas PCB is synthesized by PcyA. The pathway for PCB biosynthesis in streptophyte algae is unknown. We used phylogenetic analysis and heterologous reconstitution of bilin biosynthesis to investigate bilin biosynthesis in streptophyte algae.Phylogenetic results suggest that PcyA is present in chlorophytes and prasinophytes but absent in streptophytes. A system reconstituting bilin biosynthesis in Escherichia coli was modified to utilize HY2 from the streptophyte alga Klebsormidium flaccidum (KflaHY2). The resulting bilin was incorporated into model cyanobacterial photoreceptors and into phytochrome from the early-diverging streptophyte alga Mesostigma viride (MvirPHY1).All photoreceptors tested incorporate PCB rather than PΦB, indicating that KflaHY2 is sufficient for PCB synthesis without any other algal protein. MvirPHY1 exhibits a red–far-red photocycle similar to those seen in other streptophyte algal phytochromes.These results demonstrate that streptophyte algae use HY2 to synthesize PCB, consistent with the hypothesis that PΦB synthesis arose late in HY2 evolution.