The ribulose monophosphate pathway substitutes for the missing pentose phosphate pathway in the archaeon Thermococcus kodakaraensis
The ribulose monophosphate pathway substitutes for the missing pentose phosphate pathway in the archaeon Thermococcus kodakaraensis
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DOI：
10.1128/jb.00492-06
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发表时间：
2006-07-01
影响因子：
3.2
通讯作者：
Sakai, Yasuyoshi
中科院分区：
文献类型：
--
作者：
Orita, Izumi;Sato, Takaaki;Sakai, Yasuyoshi
单磷酸核酮糖 (RuMP) 途径涉及 3-己酮糖-6-磷酸合酶 (HPS) 和 6-磷酸-3-己酮糖异构酶 (PHI)，现已被认为是甲醛固定和解毒的广泛原核途径。有趣的是，HPS和PHI同源物也存在于多种古菌菌株中，最近的生化和基因组分析提出了这样的可能性：甲醛固定的逆反应，即从6-磷酸果糖合成5-磷酸核酮糖(Ru5P)，可能在一些戊糖磷酸途径不完善的古菌菌株中的Ru5P生物合成中发挥作用。在这项研究中，我们利用超嗜热古菌Thermococcus kodakaraensis KOD1，采用遗传学方法来解决这种可能性。该菌株拥有编码 HPS 和 PHI 融合蛋白的单一开放阅读框 (TK0475)。重组 HPS-PHI 融合酶在两个方向（甲醛固定和 Ru5P 合成）均表现出预期的 HPS 和 PHI 活性。 TK0475缺失突变体Delta hps-phi-7A在基本培养基中没有表现出任何生长，而突变株的生长可以通过向培养基中添加核苷来恢复。这种营养缺陷型表型与 HPS-PHI 融合酶的催化特性一起揭示了 HPS 和 PHI 对于核苷酸前体 Ru5P 的生物合成至关重要，表明 RuMP 途径是 Ru5P 生物合成的唯一相关途径，取代了该古菌中缺失的经典磷酸戊糖途径。
The ribulose monophosphate (RuMP) pathway, involving 3-hexulose-6-phosphate synthase (HPS) and 6-phospho-3-hexuloisomerase (PHI), is now recognized as a widespread prokaryotic pathway for formaldehyde fixation and detoxification. Interestingly, HPS and PHI homologs are also found in a variety of archaeal strains, and recent biochemical and genome analyses have raised the possibility that the reverse reaction of formaldehyde fixation, i.e., ribulose 5-phosphate (Ru5P) synthesis from fructose 6-phosphate, may function in the biosynthesis of Ru5P in some archaeal strains whose pentose phosphate pathways are imperfect. In this study, we have taken a genetic approach to address this possibility by using the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1. This strain possesses a single open reading frame (TK0475) encoding an HPS- and PHI-fused protein. The recombinant HPS-PHI-fused enzyme exhibited the expected HPS and PHI activities in both directions (formaldehyde fixing and Ru5P synthesizing). The TK0475 deletion mutant Delta hps-phi-7A did not exhibit any growth in minimal medium, while growth of the mutant strain could be recovered by the addition of nucleosides to the medium. This auxotrophic phenotype together with the catalytic properties of the HPS-PHI-fused enzyme reveal that HPS and PHI are essential for the biosynthesis of Ru5P, the precursor of nucleotides, showing that the RuMP pathway is the only relevant pathway for Ru5P biosynthesis substituting for the classical pentose phosphate pathway missing in this archaeon.