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Primary Processes During the Light-signal Transduction of Phototropin

Authors

  • Daisuke Matsuoka,

    1. Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Naka-ku, Sakai, Osaka, Japan
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    • Current address: Research Center for Environmental Genomics, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.

  • Tatsuya Iwata,

    1. Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya, Japan
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  • Kazunori Zikihara,

    1. Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Naka-ku, Sakai, Osaka, Japan
    2. Radiation Biology Center, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan
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  • Hideki Kandori,

    1. Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa-ku, Nagoya, Japan
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  • Satoru Tokutomi

    Corresponding author
    1. Department of Biological Science, Graduate School of Science, Osaka Prefecture University, Naka-ku, Sakai, Osaka, Japan
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*email: toxan@b.s.osakafu-u.ac.jp (Satoru Tokutomi)

Abstract

Phototropin is a blue-light photoreceptor in plants that mediates phototropism, chloroplast relocation, stomata opening and leaf expansion. Phototropin molecule has two photoreceptive domains named LOV1 (light–oxygen–voltage) and LOV2 in the N-terminus and a serine/threonine kinase domain in the C-terminus, and acts as a blue light-regulated kinase. Each LOV domain binds a flavin mononucleotide as a chromophore and undergoes unique cyclic reactions upon blue-light absorption that comprises a cysteinyl-flavin adduct formation through a triplet-excited state and a successive adduct break to revert to the initial ground state. The molecular reactions underlying the photocycle are reviewed and one of the probable molecular schemes is presented. Adduct formation alters the secondary protein structure of the LOV domains. This structural change could be transferred to the linker between the kinase domain and involved in the photoregulation of the kinase activity. The structural changes as well as the oligomeric structures seem to differ between LOV1 and LOV2, which may explain the proposed roles of each domain in the photoregulation of the kinase activity. The photoregulation mechanism of phototropin kinase is reviewed and discussed in reference to the regulation mechanism of protein kinase A, which it resembles.

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