Phosphorylation of transitory starch by α-glucan, water dikinase during starch turnover affects the surface properties and morphology of starch granules.
Glucan, water dikinase (GWD) is a key enzyme of starch metabolism but the physico-chemical properties of starches isolated from GWD-deficient plants and their implications for starch metabolism have so far not been described. Transgenic Arabidopsis thaliana plants with reduced or no GWD activity were used to investigate the properties of starch granules. In addition, using various in vitro assays, the action of recombinant GWD, β-amylase, isoamylase and starch synthase 1 on the surface of native starch granules was analysed. The internal structure of granules isolated from GWD mutant plants is unaffected, as thermal stability, allomorph, chain length distribution and density of starch granules were similar to wild-type. However, short glucan chain residues located at the granule surface dominate in starches of transgenic plants and impede GWD activity. A similarly reduced rate of phosphorylation by GWD was also observed in potato tuber starch fractions that differ in the proportion of accessible glucan chain residues at the granule surface. A model is proposed to explain the characteristic morphology of starch granules observed in GWD transgenic plants. The model postulates that the occupancy rate of single glucan chains at the granule surface limits accessibility to starch-related enzymes.
Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.|Biopolymers Analytics, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Sebastian
S
Mahlow
Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Mahdi
M
Hejazi
Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Franziska
F
Kuhnert
Photonics, Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Andreas
A
Garz
Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Henrike
H
Brust
Zoophysiology, Institute of Biochemistry and Biology, University of Potdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Otto
O
Baumann
Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.|Biopolymers Analytics, Institute of Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476, Potsdam-Golm, Germany.
Joerg
J
Fettke
D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D007517:Isoamylase / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D017866:Phosphotransferases (Paired Acceptors) / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011198:Solanum tuberosum; D013213:Starch / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013499:Surface Properties; D001614:beta-Amylase / Q000378:metabolism
D029681:Arabidopsis Proteins; D005964:Glucosyltransferases; D007517:Isoamylase; D009004:Monosaccharide Transport Proteins; D017866:Phosphotransferases (Paired Acceptors); D013213:Starch; D001614:beta-Amylase; C000597589:SS1 protein, Arabidopsis; C435922:At1g10760 protein, Arabidopsis; C500668:alpha-glucan, water dikinase, Arabidopsis
Arabidopsis thaliana; glucan; sex1-8; starch granule surface; starch phosphorylation; water dikinase (GWD)