Trans-membrane Signaling in Photosynthetic State Transitions: REDOX- AND STRUCTURE-DEPENDENT INTERACTION IN VITRO BETWEEN STT7 KINASE AND THE CYTOCHROME b6f COMPLEX.

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TitleTrans-membrane Signaling in Photosynthetic State Transitions: REDOX- AND STRUCTURE-DEPENDENT INTERACTION IN VITRO BETWEEN STT7 KINASE AND THE CYTOCHROME b6f COMPLEX.
Publication TypeJournal Article
Year of Publication2016
AuthorsSingh, SK, S Hasan, S, Zakharov, SD, Naurin, S, Cohn, W, Ma, J, Whitelegge, JP, Cramer, WA
JournalJ Biol Chem
Volume291
Issue41
Pagination21740-21750
Date Published2016 Oct 07
ISSN1083-351X
KeywordsChlamydomonas reinhardtii, Cytochrome b6f Complex, Light-Harvesting Protein Complexes, Oxidation-Reduction, Protein Structure, Quaternary, Protein-Serine-Threonine Kinases, Structure-Activity Relationship
Abstract

Trans-membrane signaling involving a serine/threonine kinase (Stt7 in Chlamydomonas reinhardtii) directs light energy distribution between the two photosystems of oxygenic photosynthesis. Oxidation of plastoquinol mediated by the cytochrome bf complex on the electrochemically positive side of the thylakoid membrane activates the kinase domain of Stt7 on the trans (negative) side, leading to phosphorylation and redistribution ("state transition") of the light-harvesting chlorophyll proteins between the two photosystems. The molecular description of the Stt7 kinase and its interaction with the cytochrome bf complex are unknown or unclear. In this study, Stt7 kinase has been cloned, expressed, and purified in a heterologous host. Stt7 kinase is shown to be active in vitro in the presence of reductant and purified as a tetramer, as determined by analytical ultracentrifugation, electron microscopy, and electrospray ionization mass spectrometry, with a molecular weight of 332 kDa, consisting of an 83.41-kDa monomer. Far-UV circular dichroism spectra show Stt7 to be mostly α-helical and document a physical interaction with the bf complex through increased thermal stability of Stt7 secondary structure. The activity of wild-type Stt7 and its Cys-Ser mutant at positions 68 and 73 in the presence of a reductant suggest that the enzyme does not require a disulfide bridge for its activity as suggested elsewhere. Kinase activation in vivo could result from direct interaction between Stt7 and the bf complex or long-range reduction of Stt7 by superoxide, known to be generated in the bf complex by quinol oxidation.

DOI10.1074/jbc.M116.732545
Alternate JournalJ. Biol. Chem.
PubMed ID27539852
PubMed Central IDPMC5076842
Grant ListP30 CA023168 / CA / NCI NIH HHS / United States
P30 DK063491 / DK / NIDDK NIH HHS / United States
R01 GM038323 / GM / NIGMS NIH HHS / United States