Glucan, water dikinase phosphorylates crystalline maltodextrins and thereby initiates solubilization

Authors

  • Mahdi Hejazi,

    1. UP Transfer GmbH, Am Neuen Palais 10, Building 6, 14469 Potsdam, Germany,
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  • Joerg Fettke,

    1. Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, 14476 Potsdam-Golm, Germany,
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  • Sophie Haebel,

    1. Interdisciplinary Center of Mass Spectrometry of Biopolymers, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, 14476 Potsdam-Golm, Germany,
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  • Christoph Edner,

    1. Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, 14476 Potsdam-Golm, Germany,
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  • Oskar Paris,

    1. Department of Biomaterials, Max-Planck Institute of Colloids and Surfaces, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany, and
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  • Claus Frohberg,

    1. Bayer Bioscience GmbH, Hermannswerder 20, 14473 Potsdam, Germany
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  • Martin Steup,

    Corresponding author
    1. Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, 14476 Potsdam-Golm, Germany,
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  • Gerhard Ritte

    1. Department of Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Building 20, 14476 Potsdam-Golm, Germany,
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    • Present address: Metanomics GmbH, Tegeler Weg 33, 10589 Berlin, Germany.


*(fax +49 331 977 2512; e-mail msteup@rz.uni-potsdam.de).

Summary

Starch phosphorylation by glucan, water dikinase (GWD; EC 2.7.9.4) is an essential step in the breakdown of native starch particles, but the underlying mechanisms have remained obscure. In this paper, the initial reactions of starch degradation were analyzed using crystallized maltodextrins as model carbohydrates. As revealed by X-ray diffraction analysis, the crystallized maltodextrins represent the B-type starch allomorph. Recombinant GWD phosphorylated crystalline maltodextrins with a high specific activity (55–60 nmol mg−1 protein min−1), but exhibited very little activity with the same maltodextrins that had been solubilized by heat treatment. Recombinant phosphoglucan, water dikinase (PWD; EC 2.7.9.5) utilized the crystalline maltodextrins only when pre-phosphorylated by GWD. Phosphorylation of crystalline maltodextrins, as catalyzed by GWD, initiated solubilization of neutral as well as phosphorylated glucans. In both the insoluble and the soluble state, mono-, di- and triphosphorylated α-glucans were observed, with wide and overlapping ranges of degree of polymerization. Thus, the substrate specificity of the GWD is defined by the physical arrangement of α-glucans rather than by structural parameters, such as the distribution of branching points or degree of polymerization. Unlike GWD and PWD, recombinant β-amylase isozyme 3 (BAM3), which has been shown to be essential for plastidial starch degradation, preferentially degraded soluble maltodextrins rather than crystallized glucans. In summary, two conclusions were reached. Firstly, carbohydrate targets of GWD are primarily defined by the molecular order of glucan helices. Secondly, GWD-catalyzed phosphorylation mediates the phase transition of glucans from a highly ordered to a less ordered and hydrated state.

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