title: The ADP-glucose binding site of the Escherichia coli glycogen synthase.
abstract: Bacterial glycogen/starch synthases are retaining GT-B glycosyltransferases that transfer glucosyl units from ADP-Glc to the non-reducing end of glycogen or starch. We modeled the Escherichia coli glycogen synthase based on the coordinates of the inactive form of the Agrobacterium tumefaciens glycogen synthase and the active form of the maltodextrin phosphorylase, a retaining GT-B glycosyltransferase belonging to a different family. In this model, we identified a set of conserved residues surrounding the sugar nucleotide substrate, and we replaced them with different amino acids by means of site-directed mutagenesis. Kinetic analysis of the mutants revealed the involvement of these residues in ADP-Glc binding. Replacement of Asp21, Asn246 or Tyr355 for Ala decreased the apparent affinity for ADP-Glc 18-, 45-, and 31-fold, respectively. Comparison with other crystallized retaining GT-B glycosyltransferases confirmed the striking similarities among this group of enzymes even though they use different substrates.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Yep
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Ballicora
authors.forename: Jack
authors.initials: J
authors.lastname: Preiss
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000737:chemistry*; D000595:Amino Acid Sequence; D001665:Binding Sites; D003198:Computer Simulation; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006006:Glycogen Synthase / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding
chemical_list: D029968:Escherichia coli Proteins; D000245:Adenosine Diphosphate Glucose; D006006:Glycogen Synthase