Skov, Lars K2; Pizzut-Serin, Sandra5; Remaud-Simeon, Magali5; Ernst, Heidi A6; Gajhede, Michael7; Mirza, Osman Asghar7
1 Biostructural Research, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet2 Novozymes A/S3 Universite de Toulouse4 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet5 Universite de Toulouse6 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet7 Biostructural Research, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet
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.
Acta Crystallographica. Section F: Structural Biology and Crystallization Communications Online, 2013, Vol 69, Issue Pt 9, p. 973-8