Oligosaccharide binding in Escherichia coli glycogen synthase.
Glycogen/starch synthase elongates glucan chains and is the key enzyme in the synthesis of glycogen in bacteria and starch in plants. Cocrystallization of Escherichia coli wild-type glycogen synthase (GS) with substrate ADPGlc and the glucan acceptor mimic HEPPSO produced a closed form of GS and suggests that domain-domain closure accompanies glycogen synthesis. Cocrystallization of the inactive GS mutant E377A with substrate ADPGlc and oligosaccharide results in the first oligosaccharide-bound glycogen synthase structure. Four bound oligosaccharides are observed, one in the interdomain cleft (G6a) and three on the N-terminal domain surface (G6b, G6c, and G6d). Extending from the center of the enzyme to the interdomain cleft opening, G6a mostly interacts with the highly conserved N-terminal domain residues lining the cleft of GS. The surface-bound oligosaccharides G6c and G6d have less interaction with enzyme and exhibit a more curled, helixlike structural arrangement. The observation that oligosaccharides bind only to the N-terminal domain of GS suggests that glycogen in vivo probably binds to only one side of the enzyme to ensure unencumbered interdomain movement, which is required for efficient, continuous glucan-chain synthesis.
Sheng
Fang
F
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Yep
Alejandra
A
Feng
Lei
L
Preiss
Jack
J
Geiger
James H
JH
D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D006006:Glycogen Synthase / Q000737:chemistry* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
D029968:Escherichia coli Proteins; D009844:Oligosaccharides; C016549:maltohexaose; D006006:Glycogen Synthase