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Published on: August 19, 2021
Oligosaccharide binding in Escherichia coli glycogen synthase
Fang Sheng1, Alejandra Yep, Lei Feng
1Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Biochemistry
|September 19, 2009
Summary
Glycogen synthase (GS) undergoes a domain closure during glycogen synthesis. Oligosaccharide binding to only one side of GS suggests a mechanism for efficient, continuous glucan chain elongation.
Area of Science:
- Biochemistry
- Structural Biology
- Enzymology
Background:
- Glycogen/starch synthase (GS) is crucial for synthesizing glycogen in bacteria and starch in plants by elongating glucan chains.
- Understanding the structural dynamics of GS during substrate binding is key to elucidating its catalytic mechanism.
Purpose of the Study:
- To investigate the structural changes in glycogen synthase (GS) upon binding of its substrate and acceptor.
- To determine the binding sites of oligosaccharides on glycogen synthase (GS) and their implications for enzyme function.
Main Methods:
- Cocrystallization of wild-type Escherichia coli glycogen synthase (GS) with ADPGlc and HEPPSO.
- Cocrystallization of an inactive GS mutant (E377A) with ADPGlc and oligosaccharides.
- X-ray crystallography to determine the structures of the cocrystallized complexes.
Main Results:
- Cocrystallization of wild-type GS revealed a closed enzyme form, suggesting domain-domain closure during synthesis.
- The first structure of oligosaccharide-bound GS was obtained using an inactive mutant, showing four bound oligosaccharides.
- Oligosaccharides primarily bound to the N-terminal domain, with one in the interdomain cleft and three on the surface.
Conclusions:
- Domain-domain closure is likely integral to the glycogen synthesis process catalyzed by GS.
- The specific binding of oligosaccharides to the N-terminal domain suggests a unidirectional binding mode in vivo.
- This binding mode ensures unencumbered interdomain movement, facilitating efficient and continuous glucan chain elongation.
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