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Article

Oligosaccharide Binding in Escherichia coli Glycogen Synthase

Supporting Info

Fang Sheng¶, Alejandra Yep

, Lei Feng, Jack Preiss and James H. Geiger*

^§ Department of Chemistry

Department of Biochemistry and Molecular Biology

Michigan State University, East Lansing, Michigan 48824.

Current address: College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109.

^¶ Current address: Department of Chemistry and Biochemistry, University of California Los Angeles, 611 Charles Young Dr. East, Los Angeles, California 90095-1569.

Biochemistry, 2009, 48 (42), pp 10089–10097

DOI: 10.1021/bi900916t

Publication Date (Web): September 17, 2009

*To whom correspondence should be addressed. Telephone: (517) 355-9715, ext. 234. Fax: (517) 355-1793. E-mail: geiger@cem.msu.edu.

Abstract

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.

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