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Glucan, water dikinase activity stimulates breakdown of starch granules by plastidial β-amylases

journal contribution
posted on 2023-05-18, 11:20 authored by Edner, C, Li, J, Albrecht, T, Mahlow, S, Hejazi, M, Hussain, H, Kaplan, F, Guy, C, Steven SmithSteven Smith, Steup, M, Ritte, G
Glucan phosphorylating enzymes are required for normal mobilization of starch in leaves of Arabidopsis (Arabidopsis thaliana) and potato (Solanum tuberosum), but mechanisms underlying this dependency are unknown. Using two different activity assays, we aimed to identify starch degrading enzymes from Arabidopsis, whose activity is affected by glucan phosphorylation. Breakdown of granular starch by a protein fraction purified from leaf extracts increased approximately 2-fold if the granules were simultaneously phosphorylated by recombinant potato glucan, water dikinase (GWD). Using matrix-assisted laser-desorption ionization mass spectrometry several putative starch-related enzymes were identified in this fraction, among them β-AMYLASE1 (BAM1; At3g23920) and ISOAMYLASE3 (ISA3; At4g09020). Experiments using purified recombinant enzymes showed that BAM1 activity with granules similarly increased under conditions of simultaneous starch phosphorylation. Purified recombinant potato ISA3 (StISA3) did not attack the granular starch significantly with or without glucan phosphorylation. However, starch breakdown by a mixture of BAM1 and StISA3 was 2 times higher than that by BAM1 alone and was further enhanced in the presence of GWD and ATP. Similar to BAM1, maltose release from granular starch by purified recombinant BAM3 (At4g17090), another plastid-localized β-amylase isoform, increased 2- to 3-fold if the granules were simultaneously phosphorylated by GWD. BAM activity in turn strongly stimulated the GWD-catalyzed phosphorylation. The interdependence between the activities of GWD and BAMs offers an explanation for the severe starch excess phenotype of GWD-deficient mutants.

History

Publication title

Plant Physiology

Volume

145

Pagination

17-28

ISSN

0032-0889

Department/School

School of Natural Sciences

Publisher

Amer Soc Plant Biologists

Place of publication

15501 Monona Drive, Rockville, USA, Md, 20855

Rights statement

Copyright 2007 American Society of Plant Biologists

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the biological sciences

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