Ultrafast Red Light Activation of Synechocystis Phytochrome Cph1 Triggers Major Structural Change to Form the Pfr Signalling-Competent State

Derren J. Heyes, Basile Khara, Michiyo Sakuma, Samantha J O Hardman, Ronan O'Cualain, Stephen E J Rigby, Nigel S. Scrutton

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Phytochromes are dimeric photoreceptors that regulate a range of responses in plants and microorganisms through interconversion of red light-absorbing (Pr) and far-red light-absorbing (Pfr) states. Photoconversion between these states is initiated by light-driven isomerization of a bilin cofactor, which triggers protein structural change. The extent of this change, and how light-driven structural changes in the N-terminal photosensory region are transmitted to the C-terminal regulatory domain to initiate the signalling cascade, is unknown. We have used pulsed electron-electron double resonance (PELDOR) spectroscopy to identify multiple structural transitions in a phytochrome from Synechocystis sp. PCC6803 (Cph1) by measuring distances between nitroxide labels introduced into the protein. We show that monomers in the Cph1 dimer are aligned in a parallel 'head-to-head' arrangement and that photoconversion between the Pr and Pfr forms involves conformational change in both the N- and C-terminal domains of the protein. Cryo-trapping and kinetic measurements were used to probe the extent and temporal properties of protein motions for individual steps during photoconversion of Cph1. Formation of the primary photoproduct Lumi-R is not affected by changes in solvent viscosity and dielectric constant. Lumi-R formation occurs at cryogenic temperatures, consistent with their being no major structural reorganization of Cph1 during primary photoproduct formation. All remaining steps in the formation of the Pfr state are affected by solvent viscosity and dielectric constant and occur only at elevated temperatures, implying involvement of a series of long-range solvent-coupled conformational changes in Cph1. We show that signalling is achieved through ultrafast photoisomerization where localized structural change in the GAF domain is transmitted and amplified to cause larger-scale and slower conformational change in the PHY and histidine kinase domains. This hierarchy of timescales and extent of structural change orientates the histidine kinase domain to elicit the desired light-activated biological response. © 2012 Heyes et al.
    Original languageEnglish
    Article numbere52418
    JournalPLoS ONE
    Volume7
    Issue number12
    DOIs
    Publication statusPublished - 29 Dec 2012

    Research Beacons, Institutes and Platforms

    • Manchester Institute of Biotechnology

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