7rzw | pdb_00007rzw
CryoEM structure of Arabidopsis thaliana phytochrome B
Structural highlights
Function[PHYB_ARATH] Regulatory photoreceptor which exists in two forms that are reversibly interconvertible by light: the Pr form that absorbs maximally in the red region of the spectrum and the Pfr form that absorbs maximally in the far-red region. Photoconversion of Pr to Pfr induces an array of morphogenetic responses, whereas reconversion of Pfr to Pr cancels the induction of those responses. Pfr controls the expression of a number of nuclear genes including those encoding the small subunit of ribulose-bisphosphate carboxylase, chlorophyll A/B binding protein, protochlorophyllide reductase, rRNA, etc. It also controls the expression of its own gene(s) in a negative feedback fashion. Involved in the flowering time regulation.[1] [2] Publication Abstract from PubMedMany aspects of plant photoperception are mediated by the phytochrome (Phy) family of bilin-containing photoreceptors that reversibly interconvert between inactive Pr and active Pfr conformers(1,2). Despite extensive biochemical studies, full understanding of plant Phy signalling has remained unclear due to the absence of relevant 3D models. Here we report a cryo-electron microscopy structure of Arabidopsis PhyB in the Pr state that reveals a topologically complex dimeric organization that is substantially distinct from its prokaryotic relatives. Instead of an anticipated parallel architecture, the C-terminal histidine-kinase-related domains (HKRDs) associate head-to-head, whereas the N-terminal photosensory regions associate head-to-tail to form a parallelogram-shaped platform with near two-fold symmetry. The platform is internally linked by the second of two internal Per/Arnt/Sim domains that binds to the photosensory module of the opposing protomer and a preceding 'modulator' loop that assembles tightly with the photosensory module of its own protomer. Both connections accelerate the thermal reversion of Pfr back to Pr, consistent with an inverse relationship between dimer assembly and Pfr stability. Lopsided contacts between the HKRDs and the platform create profound asymmetry to PhyB that might imbue distinct signalling potentials to the protomers. We propose that this unique structural dynamism creates an extensive photostate-sensitive surface for conformation-dependent interactions between plant Phy photoreceptors and their signalling partners. Plant phytochrome B is an asymmetric dimer with unique signalling potential.,Li H, Burgie ES, Gannam ZTK, Li H, Vierstra RD Nature. 2022 Apr;604(7904):127-133. doi: 10.1038/s41586-022-04529-z. Epub 2022, Mar 30. PMID:35355010[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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