Multiple Glycogen-binding Sites in Eukaryotic Glycogen Synthase Are Required for High Catalytic Efficiency toward Glycogen

Journal Article · Mon Dec 10 04:00:00 EST 2012 · J. Biol. Chem.

DOI:https://doi.org/10.1074/jbc.M111.264531· OSTI ID:1046233

Baskaran, Sulochanadevi; Chikwana, Vimbai M; Contreras, Christopher J; Davis, Keri D; Wilson, Wayne A; DePaoli-Roach, Anna A; Roach, Peter J; Hurley, Thomas D ^[1]

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1. Indiana-Med

Glycogen synthase is a rate-limiting enzyme in the biosynthesis of glycogen and has an essential role in glucose homeostasis. The three-dimensional structures of yeast glycogen synthase (Gsy2p) complexed with maltooctaose identified four conserved maltodextrin-binding sites distributed across the surface of the enzyme. Site-1 is positioned on the N-terminal domain, site-2 and site-3 are present on the C-terminal domain, and site-4 is located in an interdomain cleft adjacent to the active site. Mutation of these surface sites decreased glycogen binding and catalytic efficiency toward glycogen. Mutations within site-1 and site-2 reduced the V{sub max}/S{sub 0.5} for glycogen by 40- and 70-fold, respectively. Combined mutation of site-1 and site-2 decreased the V{sub max}/S{sub 0.5} for glycogen by >3000-fold. Consistent with the in vitro data, glycogen accumulation in glycogen synthase-deficient yeast cells ({Delta}gsy1-gsy2) transformed with the site-1, site-2, combined site-1/site-2, or site-4 mutant form of Gsy2p was decreased by up to 40-fold. In contrast to the glycogen results, the ability to utilize maltooctaose as an in vitro substrate was unaffected in the site-2 mutant, moderately affected in the site-1 mutant, and almost completely abolished in the site-4 mutant. These data show that the ability to utilize maltooctaose as a substrate can be independent of the ability to utilize glycogen. Our data support the hypothesis that site-1 and site-2 provide a 'toehold mechanism,' keeping glycogen synthase tightly associated with the glycogen particle, whereas site-4 is more closely associated with positioning of the nonreducing end during catalysis.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: NIH
• OSTI ID: 1046233
• Journal Information: J. Biol. Chem., Journal Name: J. Biol. Chem. Journal Issue: (39) ; 09, 2011 Vol. 286; ISSN JBCHA3; ISSN 0021-9258
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
60 APPLIED LIFE SCIENCES
BIOSYNTHESIS
CATALYSIS
ENZYMES
GLUCOSE
GLYCOGEN
HOMEOSTASIS
HYPOTHESIS
IN VITRO
MUTANTS
MUTATIONS
POSITIONING
SUBSTRATES
SURFACES
YEASTS