title: Structure of the Arabidopsis glucan phosphatase like sex four2 reveals a unique mechanism for starch dephosphorylation.
abstract: Starch is a water-insoluble, Glc-based biopolymer that is used for energy storage and is synthesized and degraded in a diurnal manner in plant leaves. Reversible phosphorylation is the only known natural starch modification and is required for starch degradation in planta. Critical to starch energy release is the activity of glucan phosphatases; however, the structural basis of dephosphorylation by glucan phosphatases is unknown. Here, we describe the structure of the Arabidopsis thaliana starch glucan phosphatase like sex four2 (LSF2) both with and without phospho-glucan product bound at 2.3Å and 1.65Å, respectively. LSF2 binds maltohexaose-phosphate using an aromatic channel within an extended phosphatase active site and positions maltohexaose in a C3-specific orientation, which we show is critical for the specific glucan phosphatase activity of LSF2 toward native Arabidopsis starch. However, unlike other starch binding enzymes, LSF2 does not possess a carbohydrate binding module domain. Instead we identify two additional glucan binding sites located within the core LSF2 phosphatase domain. This structure is the first of a glucan-bound glucan phosphatase and provides new insights into the molecular basis of this agriculturally and industrially relevant enzyme family as well as the unique mechanism of LSF2 catalysis, substrate specificity, and interaction with starch granules.
authors.affiliation: Department of Molecular and Cellular Biochemistry and Center for Structural Biology, University of Kentucky, Lexington, Kentucky 40535-0509, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Meekins
authors.forename: Hou-Fu
authors.initials: HF
authors.lastname: Guo
authors.forename: Satrio
authors.initials: S
authors.lastname: Husodo
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Paasch
authors.forename: Travis M
authors.initials: TM
authors.lastname: Bridges
authors.forename: Diana
authors.initials: D
authors.lastname: Santelia
authors.forename: Oliver
authors.initials: O
authors.lastname: Kötting
authors.forename: Craig W
authors.initials: CW
authors.lastname: Vander Kooi
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Gentry
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D018360:Crystallography, X-Ray; D054637:Dual-Specificity Phosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013213:Starch / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D005936:Glucans; D009844:Oligosaccharides; D010710:Phosphates; C016549:maltohexaose; D013213:Starch; D054637:Dual-Specificity Phosphatases; C574400:LSF2 protein, Arabidopsis