title: The structure of amylosucrase from Deinococcus radiodurans has an unusual open active-site topology.
abstract: Amylosucrases (ASes) catalyze the formation of an α-1,4-glucosidic linkage by transferring a glucosyl unit from sucrose onto an acceptor α-1,4-glucan. To date, several ligand-bound crystal structures of wild-type and mutant ASes from Neisseria polysaccharea and Deinococcus geothermalis have been solved. These structures all display a very similar overall conformation with a deep pocket leading to the site for transglucosylation, subsite -1. This has led to speculation on how sucrose enters the active site during glucan elongation. In contrast to previous studies, the AS structure from D. radiodurans presented here has a completely empty -1 subsite. This structure is strikingly different from other AS structures, as an active-site-lining loop comprising residues Leu214-Asn225 is found in a previously unobserved conformation. In addition, a large loop harbouring the conserved active-site residues Asp133 and Tyr136 is disordered. The result of the changed loop conformations is that the active-site topology is radically changed, leaving subsite -1 exposed and partially dismantled. This structure provides novel insights into the dynamics of ASes and comprises the first structural support for an elongation mechanism that involves considerable conformational changes to modulate accessibility to the sucrose-binding site and thereby allows successive cycles of glucosyl-moiety transfer to a growing glucan chain.
authors.affiliation: Novozymes A/S, Krogshøjvej 36, DK-2880 Bagsværd, Denmark.
authors.forename: Lars K
authors.initials: LK
authors.lastname: Skov
authors.forename: Sandra
authors.initials: S
authors.lastname: Pizzut-Serin
authors.forename: Magali
authors.initials: M
authors.lastname: Remaud-Simeon
authors.forename: Heidi A
authors.initials: HA
authors.lastname: Ernst
authors.forename: Michael
authors.initials: M
authors.lastname: Gajhede
authors.forename: Osman
authors.initials: O
authors.lastname: Mirza
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D034301:Deinococcus / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013395:Sucrose / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005936:Glucans; D011994:Recombinant Proteins; D013395:Sucrose; C040088:1,4-glucan; D005964:Glucosyltransferases; C019700:amylosucrase
keywords: GH13; active-site topology; amylosucrase; glucan synthesis