title: Dynamic structural changes underpin photoconversion of a blue/green cyanobacteriochrome between its dark and photoactivated states.
abstract: The phytochrome superfamily of photoreceptors exploits reversible light-driven changes in the bilin chromophore to initiate a variety of signaling cascades. The nature of these alterations and how they impact the protein moiety remain poorly resolved and might include several species-specific routes. Here, we provide a detailed picture of photoconversion for the photosensing cGMP phosphodiesterase/adenylyl cyclase/FhlA (GAF) domain from Thermosynechococcus elongatus (Te) PixJ, a member of the cyanobacteriochrome clade. Solution NMR structures of the blue light-absorbing dark state Pb and green light-absorbing photoactivated state Pg, combined with paired crystallographic models, revealed that the bilin and GAF domain dynamically transition via breakage of the C10/Cys-494 thioether bond, opposite rotations of the A and D pyrrole rings, sliding of the bilin in the GAF pocket, and the appearance of an extended region of disorder that includes Cys-494. Changes in GAF domain backbone dynamics were also observed that are likely important for inter-domain signal propagation. Taken together, photoconversion of T. elongatus PixJ from Pb to Pg involves complex structural changes within the GAF domain pocket that transduce light into a mechanical signal, many aspects of which should be relevant to others within the extended phytochrome superfamily.
authors: From the National Magnetic Resonance Facility at Madison, Department of Biochemistry and.
authors: Claudia C
authors: CC
authors: Cornilescu
authors: Gabriel
authors: G
authors: Cornilescu
authors: E Sethe
authors: ES
authors: Burgie
authors: John L
authors: JL
authors: Markley
authors: Andrew T
authors: AT
authors: Ulijasz
authors: Richard D
authors: RD
authors: Vierstra
mesh_terms: D001654:Bile Pigments / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D003624:Darkness; D008027:Light; D055537:Light Signal Transduction / Q000502:physiology*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010834:Phytochrome / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism; D046940:Synechococcus / Q000737:chemistry* / Q000201:enzymology* / Q000235:genetics
chemical_list: D001654:Bile Pigments; D013440:Sulfides; D010834:Phytochrome
keywords: Bilin; Cyanobacteria; Cyanobacteriochrome; NMR; Photoconversion; Photoreceptor; Phototransduction; Phytochrome; Plant; Protein Structure