Sheng Fang, Jia Xiaofei, Yep Alejandra, Preiss Jack, Geiger James H
Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
J Biol Chem. 2009 Jun 26;284(26):17796-807. doi: 10.1074/jbc.M809804200. Epub 2009 Feb 25.
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.
大肠杆菌糖原合酶（EcGS，EC 2.4.1.21）是一种保留型糖基转移酶（GT），它将来自二磷酸腺苷葡萄糖的葡萄糖转移到葡聚糖链受体上，同时在异头碳上保留构型。EcGS属于GT-B结构超家族。在此，我们报告了几个EcGS的X射线结构，这些结构共同为这些酶的结构和功能提供了相当多的信息。与ADP和葡萄糖结合的野生型酶的结构显示整体结构域间有15.2度的闭合，首次提供了糖原合酶催化活性闭合构象的结构。结构表明，His-161、Arg-300和Lys-305的主链羰基在转糖基化过程中作为关键催化残基。之前认为具有催化作用的Glu-377位于葡萄糖的α面上，在活性位点起静电作用并作为葡萄糖环定位器。这也与EcGS(E377A)-ADP-HEPPSO复合物的结构一致，在该复合物中，活性位点要么不存在葡萄糖部分，要么葡萄糖部分无序。
