title: The phosphoglucan phosphatase like sex Four2 dephosphorylates starch at the C3-position in Arabidopsis.
abstract: Starch contains phosphate covalently bound to the C6-position (70 to 80% of total bound phosphate) and the C3-position (20 to 30%) of the glucosyl residues of the amylopectin fraction. In plants, the transient phosphorylation of starch renders the granule surface more accessible to glucan hydrolyzing enzymes and is required for proper starch degradation. Phosphate also confers desired properties to starch-derived pastes for industrial applications. In Arabidopsis thaliana, the removal of phosphate by the glucan phosphatase Starch Excess4 (SEX4) is essential for starch breakdown. We identified a homolog of SEX4, LSF2 (Like Sex Four2), as a novel enzyme involved in starch metabolism in Arabidopsis chloroplasts. Unlike SEX4, LSF2 does not have a carbohydrate binding module. Nevertheless, it binds to starch and specifically hydrolyzes phosphate from the C3-position. As a consequence, lsf2 mutant starch has elevated levels of C3-bound phosphate. SEX4 can release phosphate from both the C6- and the C3-positions, resulting in partial functional overlap with LSF2. However, compared with sex4 single mutants, the lsf2 sex4 double mutants have a more severe starch-excess phenotype, impaired growth, and a further change in the proportion of C3- and C6-bound phosphate. These findings significantly advance our understanding of the metabolism of phosphate in starch and provide innovative options for tailoring novel starches with improved functionality for industry.
authors.affiliation: Institute for Agricultural Sciences, ETH Zurich, 8092 Zurich, Switzerland. dsantelia@ethz.ch
authors.forename: Diana
authors.initials: D
authors.lastname: Santelia
authors.forename: Oliver
authors.initials: O
authors.lastname: Kötting
authors.forename: David
authors.initials: D
authors.lastname: Seung
authors.forename: Mario
authors.initials: M
authors.lastname: Schubert
authors.forename: Matthias
authors.initials: M
authors.lastname: Thalmann
authors.forename: Sylvain
authors.initials: S
authors.lastname: Bischof
authors.forename: David A
authors.initials: DA
authors.lastname: Meekins
authors.forename: Andy
authors.initials: A
authors.lastname: Lutz
authors.forename: Nicola
authors.initials: N
authors.lastname: Patron
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Gentry
authors.forename: Frédéric H-T
authors.initials: FH
authors.lastname: Allain
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Zeeman
mesh_terms: D000687:Amylopectin / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D054637:Dual-Specificity Phosphatases / Q000235:genetics / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D010641:Phenotype; D010710:Phosphates / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013213:Starch / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000687:Amylopectin; D029681:Arabidopsis Proteins; D054637:Dual-Specificity Phosphatases; D005936:Glucans; D010710:Phosphates; D013213:Starch; C574400:LSF2 protein, Arabidopsis; C553186:At3g52180 protein, Arabidopsis
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