The Crystal Structures of the Open and Catalytically Competent Closed Conformation of Escherichia coli Glycogen Synthase

Fang Sheng,Xiaofei Jia,Alejandra Yep,Jack Preiss,James H Geiger

doi:10.1074/jbc.m809804200

Fang Sheng, Xiaofei Jia + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m809804200

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Abstract

Escherichia coli glycogen synthase (EcGS, EC 2.4.1.21) is a retaining glycosyltransferase (GT) that transfers glucose from adenosine diphosphate glucose to a glucan chain acceptor with retention of configuration at the anomeric carbon. EcGS belongs to the GT-B structural superfamily. Here we report several EcGS x-ray structures that together shed considerable light on the structure and function of these enzymes. The structure of the wild-type enzyme bound to ADP and glucose revealed a 15.2 degrees overall domain-domain closure and provided for the first time the structure of the catalytically active, closed conformation of a glycogen synthase. The main chain carbonyl group of His-161, Arg-300, and Lys-305 are suggested by the structure to act as critical catalytic residues in the transglycosylation. Glu-377, previously thought to be catalytic is found on the alpha-face of the glucose and plays an electrostatic role in the active site and as a glucose ring locator. This is also consistent with the structure of the EcGS(E377A)-ADP-HEPPSO complex where the glucose moiety is either absent or disordered in the active site.

Highlights

The biosynthesis of starch in plants and glycogen in bacteria is accomplished in three steps [1, 2]
Overall Molecular Organization—A total of four distinct structures are reported here: an apo, open form; a closed form, wild-type EcGS (wtGS) bound to ADP, glucose, and HEPPSO; wtGS bound to ADP, an unidentified glucose derivative; and HEPPSO and E. coli glycogen synthases (GS) E377A bound to ADP and HEPPSO
Comparison of the Open ADP-bound AtGS and the Closed ADP/Glucose-bound EcGS—GS differs from all other GT-B retaining enzymes whose structures are known by the very large interdomain motion accompanied by substrate binding

Summary

Introduction

The biosynthesis of starch in plants and glycogen in bacteria is accomplished in three steps [1, 2]. The HEPPSO O5 was anomeric carbon of the glucose moiety of ADP, indicating that close to the KTGGL motif loop and makes a 2.9-Å hydrogen the phosphate-glucosyl bond had been broken.

Results

Conclusion