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

  • 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 EscherichiaControlled 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.show moreshow less

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Author details:Christian Ruzanski, Julia Smirnova, Martin Rejzek, Darrell Cockburn, Henriette L. Pedersen, Marilyn Pike, William G. T. Willats, Birte Svensson, Martin SteupORCiDGND, Oliver Ebenhöh, Alison M. Smith, Robert A. Field
DOI:https://doi.org/10.1074/jbc.M113.497867
ISSN:0021-9258
ISSN:1083-351X
Title of parent work (English):The journal of biological chemistry
Publisher:American Society for Biochemistry and Molecular Biology
Place of publishing:Bethesda
Publication type:Article
Language:English
Year of first publication:2013
Publication year:2013
Release date:2017/03/26
Tag:Carbohydrate Metabolism; Computer Modeling; Glucanotransferase; Leaf Cell; Maltose Metabolism; Metabolic Regulation; Oligosaccharide; Plant Biochemistry; Starch Degradation
Volume:288
Issue:40
Number of pages:18
First page:28581
Last Page:28598
Funding institution:Biotechnology and Biological Sciences Research Council (UK) [BB/J004561/1]; John Innes Foundation; Deutsche Forschungsgemeinschaft [SFB 429]; instrument grant (Biacore T100); Danish Council for Independent Research, Natural Sciences; Danish Technical University; Danish Council for Independent Research, Technology and Production Sciences
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Biochemie und Biologie
Peer review:Referiert
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