title: Towards the molecular understanding of glycogen elongation by amylosucrase.
abstract: Amylosucrase from Neisseria polysaccharea (AS) is a transglucosidase from the glycoside-hydrolase family 13 that catalyzes the synthesis of an amylose-like polymer from sucrose, without any primer. Its affinity towards glycogen is particularly noteworthy since glycogen is the best D-glucosyl unit acceptor and the most efficient activator (98-fold k(cat) increase) known for this enzyme. Glycogen-enzyme interactions were modeled starting from the crystallographic AS: maltoheptaose complex, where two key oligosaccharide binding sites, OB1 and OB2, were identified. Two maltoheptaose molecules were connected by an alpha-1,6 branch by molecular modeling to mimic a glycogen branching. Among the various docking positions obtained, four models were chosen based on geometry and energy criteria. Robotics calculations enabled us to describe a back and forth motion of a hairpin loop of the AS specific B'-domain, a movement that assists the elongation of glycogen branches. Modeling data combined with site-directed mutagenesis experiments revealed that the OB2 surface site provides an anchoring platform at the enzyme surface to capture the polymer and direct the branches towards the OB1 acceptor site for elongation. On the basis of the data obtained, a semiprocessive glycogen elongation mechanism can be proposed.
authors.affiliation: Laboratoire Surfaces Cellulaires et Signalisation chez les Végétaux, UMR 5546 CNRS-Université Paul Sabatier-Toulouse III, 24 Chemin de Borde Rouge, BP42617, 31326 Castanet-Tolosan, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Albenne
authors.forename: Lars K
authors.initials: LK
authors.lastname: Skov
authors.forename: Vinh
authors.initials: V
authors.lastname: Tran
authors.forename: Michael
authors.initials: M
authors.lastname: Gajhede
authors.forename: Pierre
authors.initials: P
authors.lastname: Monsan
authors.forename: Magali
authors.initials: M
authors.lastname: Remaud-Siméon
authors.forename: Gwénaëlle
authors.initials: G
authors.lastname: André-Leroux
mesh_terms: D001120:Arginine / Q000378:metabolism; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005936:Glucans / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry* / Q000378:metabolism; D006003:Glycogen / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009343:Neisseria / Q000737:chemistry / Q000201:enzymology; D010649:Phenylalanine / Q000378:metabolism; D011487:Protein Conformation; D013395:Sucrose / Q000378:metabolism
chemical_list: D005936:Glucans; C031146:maltoheptaose; D010649:Phenylalanine; D013395:Sucrose; D006003:Glycogen; D001120:Arginine; D005964:Glucosyltransferases; C019700:amylosucrase