title: Granule-bound starch synthase I. A major enzyme involved in the biogenesis of B-crystallites in starch granules.
abstract: Starch defines a semicrystalline polymer made of two different polysaccharide fractions. The A- and B-type crystalline lattices define the distinct structures reported in cereal and tuber starches, respectively. Amylopectin, the major fraction of starch, is thought to be chiefly responsible for this semicrystalline organization while amylose is generally considered as an amorphous polymer with little or no impact on the overall crystalline organization. STA2 represents a Chlamydomonas reinhardtii gene required for both amylose biosynthesis and the presence of significant granule-bound starch synthase I (GBSSI) activity. We show that this locus encodes a 69 kDa starch synthase and report the organization of the corresponding STA2 locus. This enzyme displays a specific activity an order of magnitude higher than those reported for most vascular plants. This property enables us to report a detailed characterization of amylose synthesis both in vivo and in vitro. We show that GBSSI is capable of synthesizing a significant number of crystalline structures within starch. Quantifications of amount and type of crystals synthesized under these conditions show that GBSSI induces the formation of B-type crystals either in close association with pre-existing amorphous amylopectin or by crystallization of entirely de novo synthesized material.
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, Unité Mixte de Recherche CNRS/USTL n degrees 8576, Unité Sous Contrat de l'INRA, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Wattebled
authors.forename: Alain
authors.initials: A
authors.lastname: Buléon
authors.forename: Brigitte
authors.initials: B
authors.lastname: Bouchet
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Ral
authors.forename: Luc
authors.initials: L
authors.lastname: Liénard
authors.forename: David
authors.initials: D
authors.lastname: Delvallé
authors.forename: Kim
authors.initials: K
authors.lastname: Binderup
authors.forename: David
authors.initials: D
authors.lastname: Dauvillée
authors.forename: Steven
authors.initials: S
authors.lastname: Ball
authors.forename: Christophe
authors.initials: C
authors.lastname: D'Hulst
mesh_terms: D000595:Amino Acid Sequence; D000687:Amylopectin / Q000096:biosynthesis; D000688:Amylose / Q000096:biosynthesis; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003429:Cross Reactions; D003459:Crystallins / Q000096:biosynthesis / Q000737:chemistry; D018076:DNA, Complementary; D005091:Exons; D023061:Gene Order; D007438:Introns; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013214:Starch Synthase / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*
chemical_list: D003459:Crystallins; D018076:DNA, Complementary; D010940:Plant Proteins; D000688:Amylose; D000687:Amylopectin; D013214:Starch Synthase