Dynamic structural changes underpin photoconversion of a blue/green cyanobacteriochrome between its dark and photoactivated states. Journal Article

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Authors: Cornilescu, CC; Cornilescu, G; Burgie, ES; Markley, JL; Ulijasz, AT; Vierstra, RD
Article 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.
Journal Title: The Journal of biological chemistry
ISSN: 1083-351X; 0021-9258
Publisher: Unknown  
Date Published: 2014