title: The D-ring, not the A-ring, rotates in Synechococcus OS-B' phytochrome.
abstract: Phytochrome photoreceptors in plants and microorganisms switch photochromically between two states, controlling numerous important biological processes. Although this phototransformation is generally considered to involve rotation of ring D of the tetrapyrrole chromophore, Ulijasz et al. (Ulijasz, A. T., Cornilescu, G., Cornilescu, C. C., Zhang, J., Rivera, M., Markley, J. L., and Vierstra, R. D. (2010) Nature 463, 250-254) proposed that the A-ring rotates instead. Here, we apply magic angle spinning NMR to the two parent states following studies of the 23-kDa GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domain fragment of phytochrome from Synechococcus OS-B'. Major changes occur at the A-ring covalent linkage to the protein as well as at the protein residue contact of ring D. Conserved contacts associated with the A-ring nitrogen rule out an A-ring photoflip, whereas loss of contact of the D-ring nitrogen to the protein implies movement of ring D. Although none of the methine bridges showed a chemical shift change comparable with those characteristic of the D-ring photoflip in canonical phytochromes, denaturation experiments showed conclusively that the same occurs in Synechococcus OS-B' phytochrome upon photoconversion. The results are consistent with the D-ring being strongly tilted in both states and the C15=C16 double bond undergoing a Z/E isomerization upon light absorption. More subtle changes are associated with the A-ring linkage to the protein. Our findings thus disprove A-ring rotation and are discussed in relation to the position of the D-ring, photoisomerization, and photochromicity in the phytochrome family.
authors: From the Leids Instituut voor Chemisch Onderzoek, Universiteit Leiden, NL-2300 RA Leiden, The Netherlands.
authors: Chen
authors: C
authors: Song
authors: Georgios
authors: G
authors: Psakis
authors: Jakub
authors: J
authors: Kopycki
authors: Christina
authors: C
authors: Lang
authors: Jörg
authors: J
authors: Matysik
authors: Jon
authors: J
authors: Hughes
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017785:Photons; D020283:Photoreceptors, Microbial; D010834:Phytochrome / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D051939:Phytochrome B / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000502:physiology*; D013329:Structure-Activity Relationship; D046940:Synechococcus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C413622:Cph2 protein, bacteria; D020283:Photoreceptors, Microbial; D010834:Phytochrome; D051939:Phytochrome B; D011494:Protein Kinases; C413623:Cph1 phytochrome protein, bacteria
keywords: Biophysics; Cyanobacteria; Molecular Biology; NMR; Photoisomerization; Photoreceptors; Phytochrome; Protein Structure; Structural Biology