Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 1 avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
Arch Biochem Biophys. 2011 Jan 1;505(1):1-12. doi: 10.1016/j.abb.2010.08.008. Epub 2010 Aug 13.
Glucosamine-6P synthase, which catalyzes glucosamine-6P synthesis from fructose-6P and glutamine, channels ammonia over 18Å between its glutaminase and synthase active sites. The crystal structures of the full-length Escherichia coli enzyme have been determined alone, in complex with the first bound substrate, fructose-6P, in the presence of fructose-6P and a glutamine analog, and in the presence of the glucosamine-6P product. These structures represent snapshots of reaction intermediates, and their comparison sheds light on the dynamics of catalysis. Upon fructose-6P binding, the C-terminal loop and the glutaminase domains get ordered, leading to the closure of the synthase site, the opening of the sugar ring and the formation of a "closed" ammonia channel. Then, glutamine binding leads to the closure of the Q-loop to protect the glutaminase site, the activation of the catalytic residues involved in glutamine hydrolysis, the swing of the side chain of Trp74, which allows the communication between the two active sites through an "open" channel, and the rotation of the glutaminase domains relative to the synthase domains dimer. Therefore, binding of the substrates at the appropriate reaction time is responsible for the formation and opening of the ammonia channel and for the activation of the enzyme glutaminase function.
葡萄糖胺-6P 合酶可催化果糖-6P 和谷氨酰胺合成葡萄糖胺-6P，其将氨从距离相隔 18Å 的谷氨酰胺酶和合成酶活性部位转运过来。全长大肠杆菌酶的晶体结构已被单独确定，与第一个结合的底物果糖-6P 一起确定，在存在果糖-6P 和谷氨酰胺类似物的情况下，以及在葡萄糖胺-6P 产物存在的情况下确定。这些结构代表了反应中间体的快照，它们的比较揭示了催化动力学。果糖-6P 结合后，C 端环和谷氨酰胺酶结构域变得有序，导致合成酶位点关闭，糖环打开，并形成“封闭”的氨通道。然后，谷氨酰胺结合导致 Q 环关闭以保护谷氨酰胺酶位点，参与谷氨酰胺水解的催化残基的激活，色氨酸 74 的侧链摆动，这允许通过“开放”通道在两个活性部位之间进行通讯，以及谷氨酰胺酶结构域相对于合成酶结构域二聚体的旋转。因此，在适当的反应时间结合底物负责氨通道的形成和打开，并激活酶的谷氨酰胺酶功能。
