Dynamic Structural Changes Underpin Photoconversion of a Blue/Green Cyanobacteriochrome between Its Dark and Photoactivated States |
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Authors: | Claudia C. Cornilescu Gabriel Cornilescu E. Sethe Burgie John L. Markley Andrew T. Ulijasz Richard D. Vierstra |
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Affiliation: | From the ‡National Magnetic Resonance Facility at Madison, Department of Biochemistry and ;§Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706 and ;¶MRC Centre for Molecular Bacteriology and Infection (CMBI), Imperial College London, London SW7 2AZ, United Kingdom |
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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. |
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Keywords: | Cyanobacteria NMR Phototransduction Plant Protein Structure Bilin Cyanobacteriochrome Photoconversion Photoreceptor Phytochrome |
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