Granule-bound starch synthase I. A major enzyme involved in the biogenesis of B-crystallites in starch granules.
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.
Wattebled
Fabrice
F
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.
Buléon
Alain
A
Bouchet
Brigitte
B
Ral
Jean-Philippe
JP
Liénard
Luc
L
Delvallé
David
D
Binderup
Kim
K
Dauvillée
David
D
Ball
Steven
S
D'Hulst
Christophe
C
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*
D003459:Crystallins; D018076:DNA, Complementary; D010940:Plant Proteins; D000688:Amylose; D000687:Amylopectin; D013214:Starch Synthase