title: The crystal structures of the open and catalytically competent closed conformation of Escherichia coli glycogen synthase.
abstract: Escherichia coli glycogen synthase (EcGS, EC 2.4.1.21) is a retaining glycosyltransferase (GT) that transfers glucose from adenosine diphosphate glucose to a glucan chain acceptor with retention of configuration at the anomeric carbon. EcGS belongs to the GT-B structural superfamily. Here we report several EcGS x-ray structures that together shed considerable light on the structure and function of these enzymes. The structure of the wild-type enzyme bound to ADP and glucose revealed a 15.2 degrees overall domain-domain closure and provided for the first time the structure of the catalytically active, closed conformation of a glycogen synthase. The main chain carbonyl group of His-161, Arg-300, and Lys-305 are suggested by the structure to act as critical catalytic residues in the transglycosylation. Glu-377, previously thought to be catalytic is found on the alpha-face of the glucose and plays an electrostatic role in the active site and as a glucose ring locator. This is also consistent with the structure of the EcGS(E377A)-ADP-HEPPSO complex where the glucose moiety is either absent or disordered in the active site.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Fang
authors.initials: F
authors.lastname: Sheng
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Jia
authors.forename: Alejandra
authors.initials: A
authors.lastname: Yep
authors.forename: Jack
authors.initials: J
authors.lastname: Preiss
authors.forename: James H
authors.initials: JH
authors.lastname: Geiger
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology*; D006006:Glycogen Synthase / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D000245:Adenosine Diphosphate Glucose; D006006:Glycogen Synthase