Structure of a bacteriophytochrome in two states revealed

Cryo-EM structure doctorBphP-doctorRR in Pr. a Reconstructed electron density of full length Pr doctorBphP-doctorThe RR is illustrated by the refined structural model down to the Leu591 residue. The electron density of the CA domains is below the level of the presented contour. See Supplementary Figure 5a for CA and REC field assignment. b The PHY language adopted a β-sheet form of Pr-state phytochromes. c The density of the BV chromophore favors the 15Z-conformation (compare Supplementary Figure 5c). The intensities of tongue and BV were taken from the cryo-EM map where the PSM and neck region were locally refined (Pr PSM, see Supplementary Figure 2). Credit: Nature Communication (2022). DOI: 10.1038/s41467-022-34893-3

Scientists have uncovered both dark-adapted and light-activated structures of phytochrome, a red photosensor protein.

Structural changes that are almost nonexistent in regulatory areas could cause major changes elsewhere, the study’s results show. Study published Nature Communication.

‘Nobody has done this before’

Plants and bacteria adapt to the light environment using various photoreceptor proteins. Phytochromes are a group of photoreceptors that respond to red and far-red light. The function of phytochromes has been extensively studied. Still, their exact and biologically relevant structures remain unclear.

Now, full-length structures of DrBphP, a model bacterial phytochrome from Deinococcus radiodurans, have been revealed in two activity states. “Despite many attempts, no one succeeded. [in solving] “This is why we decided to apply cryo-electron microscopy to this phytochrome model,” explains Heikki Takala from the University of Jyväskylä.

Light-induced structural changes revealed by cryogenic electron microscopy

From the University of Jyväskylä, Dr. Heikki Takala and Prof. An international team that includes the Janne Ihalainen groups has now successfully uncovered the structure of DrBphP.

Using single-particle cryo-electron microscopy (cryo-EM), they discovered that the structure of the full-length phytochrome is a symmetric and relatively well-defined dimer in the dark-adapted state. However, when illuminated with red light, the output histidine kinase module becomes asymmetrical and less pronounced.

Contrary to what was predicted in previous studies, light-induced structural changes in the photosensitive module were small but only amplified in the output module. One of the senior scientists on the team, Prof. Janne Ihalainen adds, “These results suggest that structural changes that are almost absent in regulatory domains can cause major changes elsewhere, providing valuable information about signal propagation and allostery in sensory proteins.”

More information:
Weixiao Yuan Wahlgren et al., Structural mechanism of signal transduction in a phytochrome histidine kinase, Nature Communication (2022). DOI: 10.1038/s41467-022-34893-3

Provided by the University of Jyväskylä

Quotation: Two states structure of a bacteriophytochrome revealed (2022, 20 Dec), retrieved 20 Dec 2022 from https://phys.org/news/2022-12-bacteriophytochrome-states-revealed.html.

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