PDBsum entry 3guh

Transferase

PDB id: 3guh

Contents

Protein chain

477 a.a.

Ligands

ADP

250

ASO

PE3 ×2

ACT ×2

Waters ×209

References listed in PDB file

Key reference

Title

The crystal structures of the open and catalytically competent closed conformation of escherichia coli glycogen synthase.

Authors

F.Sheng, X.Jia, A.Yep, J.Preiss, J.H.Geiger.

Ref.

J Biol Chem, 2009, 284, 17796-17807. [DOI no: 10.1074/jbc.M809804200]

PubMed id

19244233

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.

Figure 3.
A, overlay of the active site of E. coli wtGSb (in yellow and atom colored) and E377A (in green). B, structural comparison of ADP, glucose binding site, and active site residues between EcGS (in yellow and atom colored, wtGSb), MalP (blue, PDB 2asv), rabbit R-GP (pink, PDB 1gpa), OtsA (green, 1uqu), WaaG (orange, PDB 2iw1), and AGT (cyan, PDB 1y6f). MalP PO[43]^−, ASO, and maltopentaose occupied the equivalent positions of the ADP distal phosphate group, glucose, and HEPPSO in the wtGSb structure, respectively. Residues are labeled according to EcGS sequence except for AGT Glu-306. Structural alignment again using TURBO-FRODO and the Cα carbons of the active site residues. C, left, overlay of NDP-sugar in OtsA, AGT, WaaG, and ADP and glucose in wtGSb. The color scheme and PDB used are the same as described in B. Right, comparison of ligands in MalP (PDB 2asv, blue, PLP + PO[4]^3− + ASO and PDB 1l5v, red, PLP + Glc-1-P, in sticks) and in GP (PDB 1noi, lemon, PLP + PO[4]^3− + nojirimycine tetrazole; PDB 2gpb, teal, PLP + glucose; PDB 3gpb, pink, PLP + Glc-1-P, in lines).

Figure 4.
Proposed mechanisms of glucosyl transfer catalyzed by GT retaining enzymes. Two essential components of double-displacement, a catalytic nucleophile and a glucosyl-enzyme intermediate, are circled and framed, respectively. In S[n]i- and S[n]1-like mechanisms, the positively charged DGM (framed) is stabilized by the leaving group AMP-phosphate and the incoming nucleophile 4-hydroxyl group of the sugar.

The above figures are reprinted by permission from the ASBMB: J Biol Chem (2009, 284, 17796-17807) copyright 2009.