Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 10, Pages 3842-3847Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1013377108
Keywords
chromophore-protein interaction; signal transduction; solid-state NMR; photomorphogenesis
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Funding
- Volkswagen-Stiftung [I/82628]
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Phytochrome photoreceptors mediate light responses in plants and in many microorganisms. Here we report studies using H-1-C-13 magic-angle spinning NMR spectroscopy of the sensor module of cyanobacterial phytochrome Cph1. Two isoforms of the red-light absorbing Pr ground state are identified. Conclusive evidence that photoisomerization occurs at the C15-methine bridge leading to a beta-facial disposition of the ring D is presented. In the far-red-light absorbing Pfr state, strong hydrogen-bonding interactions of the D-ring carbonyl group to Tyr-263 and of N24 to Asp-207 hold the chromophore in a tensed conformation. Signaling is triggered when Asp-207 is released from its salt bridge to Arg-472, probably inducing conformational changes in the tongue region. A second signal route is initiated by partner swapping of the B-ring propionate between Arg-254 and Arg-222.
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