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Temperature-scan cryocrystallography reveals reaction intermediates in bacteriophytochrome
Xiaojing Yang1, Zhong Ren, Jane Kuk
1Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, USA. xiaojingyang@uchicago.edu
Nature
|October 18, 2011
Summary
Phytochromes convert light signals into biological responses. This study reveals the initial E-to-Z isomerization of the biliverdin chromophore in Pseudomonas aeruginosa bacteriophytochrome as the key photochemical event, driving subsequent structural changes.
Area of Science:
- Biochemistry
- Structural Biology
- Photobiology
Background:
- Phytochromes are crucial photoreceptors regulating physiological processes via reversible light absorption.
- Understanding the initial photochemical events in phytochrome photoreaction is essential for elucidating light signal transduction.
- Previous structural studies focused on dark-adapted states, lacking insights into intermediate photochemical steps.
Purpose of the Study:
- To determine the crystal structures of intermediates in the photoreaction of Pseudomonas aeruginosa bacteriophytochrome (PaBphP).
- To elucidate the initial photochemical events and subsequent structural changes upon light absorption by PaBphP.
Main Methods:
- Cryo-trapping crystallography was employed to capture transient intermediates.
- Structural changes were analyzed by varying the temperature at which the photoreaction occurred.
- Detailed structural analysis of the biliverdin chromophore and surrounding protein.
Main Results:
- Three intermediate structures in the PaBphP photoreaction cycle were determined.
- The initial photochemical event is an E-to-Z isomerization of the biliverdin (BV) chromophore's C(15)=C(16) double bond.
- Conformational changes initiate in chromophore ring D and propagate to other rings (C, B, A) and the protein.
Conclusions:
- Light absorption triggers structural signal transduction in PaBphP through chromophore isomerization and subsequent protein conformational changes.
- The study provides the first crystallographic characterization of initial photochemical events in phytochrome photoreaction.
- Understanding these initial steps is key to deciphering how light signals are converted into biological responses.
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