In higher eukaryotes and plants, the last two sequential steps in the de novo biosynthesis of uridine 5′-monophosphate (UMP) are catalyzed by a bifunctional natural chimeric protein called UMP synthase (UMPS). In higher plants, UMPS consists of two naturally fused enzymes: orotate phosphoribosyltransferase (OPRTase) at N-terminal and orotidine-5′-monophosphate decarboxylase (ODCase) at C-terminal. In this work, we obtained the full functional recombinant protein UMPS from Coffea arabica (CaUMPS) and studied its structure-function relationships. A biochemical and structural characterization of a plant UMPS with its two functional domains is described together with the presentation of the first crystal structure of a plant ODCase at 1.4 Å resolution. The kinetic parameters measured of CaOPRTase and CaODCase domains were comparable to those reported. The crystallographic structure revealed that CaODCase is a dimer that conserves the typical fold observed in other ODCases from prokaryote and eukaryote with a 1-deoxy-ribofuranose-5′-phosphate molecule bound in the active site of one subunit induced a closed conformation. Our results add to the knowledge of one of the key enzymes of the de novo biosynthesis of pyrimidines in plant metabolism and open the door to future applications.

在高等真核生物和植物中，尿苷 5'-单磷酸 (UMP)从头生物合成的最后两个连续步骤是由称为 UMP 合酶 (UMPS) 的双功能天然嵌合蛋白催化的。在高等植物中，UMPS 由两种天然融合酶组成：N 端的乳清酸磷酸核糖基转移酶 (OPRTase) 和 C 端的乳清酸 5'-单磷酸脱羧酶 (ODCase)。在这项工作中，我们从阿拉比卡咖啡中获得了全功能重组蛋白UMPS（ Ca UMPS）并研究了其结构与功能关系。描述了具有两个功能域的植物 UMPS 的生化和结构特征，并以 1.4 Å 分辨率展示了植物 ODCase 的第一个晶体结构。 Ca OPRTase 和Ca ODCase 结构域的动力学参数测量结果与报道的相当。晶体结构表明， Ca ODCase 是一种二聚体，保留了在原核生物和真核生物的其他 ODCase 中观察到的典型折叠，其中 1-脱氧-呋喃核糖-5'-磷酸分子结合在一个亚基的活性位点上，诱导闭合构象。我们的结果增加了对植物代谢中嘧啶从头生物合成的关键酶之一的了解，并为未来的应用打开了大门。