A bacterial glucanotransferase can replace the complex maltose metabolism required for starch to sucrose conversion in leaves at night

Christian Ruzanski, Julia Smirnova, Martin Rejzek, Darrell Cockburn, Henriette L Pedersen, Marilyn Pike, William G T Willats, Birte Svensson, Martin Steup, Oliver Ebenhoeh, Alison M Smith, Robert A Field

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29 Citations (Scopus)
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Controlled conversion of leaf starch to sucrose at night is essential for the normal growth of Arabidopsis. The conversion involves the cytosolic metabolism of maltose to hexose phosphates via an unusual, multidomain protein with 4-glucanotransferase activity, DPE2, believed to transfer glucosyl moieties to a complex heteroglycan prior to their conversion to hexose phosphate via a cytosolic phosphorylase. The significance of this complex pathway is unclear; conversion of maltose to hexose phosphate in bacteria proceeds via a more typical 4-glucanotransferase that does not require a heteroglycan acceptor. It has recently been suggested that DPE2 generates a heterogeneous series of terminal glucan chains on the heteroglycan that acts as a glucosyl buffer to ensure a constant rate of sucrose synthesis in the leaf at night. Alternatively, DPE2 and/or the heteroglycan may have specific properties important for their function in the plant. To distinguish between these ideas, we compared the properties of DPE2 with those of the Escherichia coli glucanotransferase MalQ. We found that MalQ cannot use the plant heteroglycan as an acceptor for glucosyl transfer. However, experimental and modeling approaches suggested that it can potentially generate a glucosyl buffer between maltose and hexose phosphate because, unlike DPE2, it can generate polydisperse malto-oligosaccharides from maltose. Consistent with this suggestion, MalQ is capable of restoring an essentially wild-type phenotype when expressed in mutant Arabidopsis plants lacking DPE2. In light of these findings, we discuss the possible evolutionary origins of the complex DPE2-heteroglycan pathway.

Original languageEnglish
Pages (from-to)28581-28598
Number of pages18
JournalThe Journal of Biological Chemistry
Issue number40
Early online date15 Aug 2013
Publication statusPublished - 4 Oct 2013


  • carbohydrate metabolism
  • computer modeling
  • metabolic regulation
  • oligosaccharide
  • plant biochemistry
  • glucanotransferase
  • leaf cell
  • maltose metabolism
  • starch degradation
  • PHO-2 phosphorylase isozyme
  • Escherichia-coli
  • cytosolic heteroglycans
  • disproportionating enzyme
  • subcellular-localization
  • arabidopsis-thaliana
  • plant
  • amylomaltase
  • degradation
  • microarrays


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