Enzymatic Properties of Futalosine Hydrolase, an Enzyme Essential to a Newly Identified Menaquinone Biosynthetic Pathway
作者:Tomoshige HIRATSUKA、Nobuya ITOH、Haruo SETO、Tohru DAIRI
DOI:10.1271/bbb.80906
日期:2009.5.23
In prokaryotes, menaquinone is used for respiration. In Escherichia coli, menaquinone is biosynthesized from chorismate by seven enzymes. However, very recently, we identified an alternative pathway (the futalosine pathway), which operates in some bacteria, including Streptomyces coelicolor, Helicobacter pylori, Campylobacter jejuni, and Thermus thermophilus. We describe the steps of this pathway, which branches at chorismate in a manner similar to the known pathway, but then follows a different route. This new pathway includes futalosine, an unusual nucleoside derivative consisting of inosine and o-substituted benzoate moieties, as a biosynthetic intermediate. In this study, a recombinant futalosine hydrolase (TTHA0556) of T. thermophilus, which participates in the second step of the pathway and catalyzes the reaction releasing hypoxanthine from futalosine, was prepared and used in functional analyses. Recombinant TTHA0556 formed a homotetramer and reacted only with futalosine; other structurally related nucleotides and nucleosides were not accepted. Recombinant TTHA0556 required no cofactors, and the optimum pH and temperature were 4.5 and 80 °C. The Km value was calculated to be 154.0±5.3 μm and the kcat value was 1.02/s. Recombinant TTHA0556 was slightly inhibited by hypoxanthine, with a Ki value of 1.1 mm.
在原核生物中,脑醌用于呼吸。在大肠杆菌中,甲萘醌是通过七种酶从壳聚糖中生物合成的。然而,最近我们发现了另一种途径(富他洛苷途径),这种途径在一些细菌中运行,包括嗜热链霉、幽门螺杆菌、空肠弯曲杆菌和嗜热菌。我们描述了这一途径的步骤,它在氯甲酸酯处的分支与已知途径相似,但随后的途径不同。这条新途径包括一种由肌苷和邻代苯甲酸酯分子组成的不同寻常的核苷衍生物--富塔罗索碱(futalosine),作为生物合成的中间体。本研究制备了嗜热菌的重组富塔罗索碱水解酶(TTHA0556)并将其用于功能分析,该酶参与该途径的第二步,并催化从富塔罗索碱释放次黄嘌呤的反应。重组的 TTHA0556 形成同源四聚体,只与富塔罗索碱反应;不接受其他结构相关的核苷酸和核苷。重组 TTHA0556 不需要辅助因子,最佳 pH 值和温度分别为 4.5 和 80 °C。计算得出的 Km 值为 154.0±5.3 μm,kcat 值为 1.02/s。重组 TTHA0556 对次黄嘌呤有轻微抑制作用,Ki 值为 1.1 mm。