Sigrell J A, Cameron A D, Mowbray S L
Department of Molecular Biology, Uppsala University, Uppsala, Sweden.
J Mol Biol. 1999 Jul 30;290(5):1009-18. doi: 10.1006/jmbi.1999.2938.
The enzyme ribokinase phosphorylates ribose at O5* as the first step in its metabolism. The original X-ray structure of Escherichia coli ribokinase represented the ternary complex including ribose and ADP. Structures are presented here for the apo enzyme, as well as the ribose-bound state and four new ternary complex forms. Combined, the structures suggest that large and small conformational changes play critical roles in the function of this kinase. An initially open apo form can allow entry of the ribose substrate. After ribose binding, the active site lid is observed in a closed conformation, with the sugar trapped underneath. This closure and associated changes in the protein appear to assist ribokinase in recognition of the co-substrate ATP as the next step. Binding of the nucleotide brings about further, less dramatic adjustments in the enzyme structure. Additional small movements are almost certainly required during the phosphoryltransfer reaction. Evidence is presented that some types of movements of the lid are allowed in the ternary complex, which may be critical to the creation and breakdown of the transition state. Similar events are likely to take place during catalysis by other related carbohydrate kinases, including adenosine kinase.
在核糖代谢的第一步中，核糖激酶将核糖在O5*位磷酸化。大肠杆菌核糖激酶最初的X射线结构代表了包含核糖和ADP的三元复合物。本文展示了无配体酶、核糖结合状态以及四种新的三元复合物形式的结构。综合来看，这些结构表明，大的和小的构象变化在这种激酶的功能中起着关键作用。最初开放的无配体形式能够允许核糖底物进入。核糖结合后，观察到活性位点盖子处于闭合构象，核糖被困在其下方。这种闭合以及蛋白质中相关的变化似乎有助于核糖激酶识别作为下一步的共底物ATP。核苷酸的结合会使酶结构发生进一步的、不太显著的调整。在磷酸转移反应过程中几乎肯定还需要额外的小移动。有证据表明，在三元复合物中盖子的某些类型的移动是允许的，这可能对过渡态的形成和分解至关重要。在包括腺苷激酶在内的其他相关碳水化合物激酶催化过程中可能会发生类似的事件。
