para-Aminobenzoic Acid Is a Precursor in Coenzyme Q6 Biosynthesis in Saccharomyces cerevisiae
para-Aminobenzoic Acid Is a Precursor in Coenzyme Q6 Biosynthesis in Saccharomyces cerevisiae
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DOI：
10.1074/jbc.m110.151894
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发表时间：
2010-09-03
影响因子：
4.8
通讯作者：
Clarke, Catherine F.
中科院分区：
文献类型：
--
作者：
Marbois, Beth;Xie, Letian X.;Clarke, Catherine F.
辅酶Q（泛醌或Q）是真核生物呼吸电子传递所需的重要线粒体脂质。4-羟基苯甲酸（4 HB）是一种芳香环前体，形成Q的苯醌环，广泛用于检测Q的生物合成。然而，在酵母中合成4 HB的直接前体化合物和酶促步骤是未知的。在这里，我们表明，对氨基苯甲酸（pABA），一个众所周知的叶酸前体，也作为Q生物合成的前体。六异戊二烯化形式的pABA（异戊二烯基-pABA）通常存在于野生型酵母粗脂质提取物中，但在缺乏pABA的酵母abz 1突变体中不存在。pABA的稳定C-13（6）-同位素（对氨基[芳香族-C-13（6）]苯甲酸（[C-13（6）]pABA））在野生型或abz 1突变酵母中被异戊烯化以形成异戊烯基-[C-13（6）]pABA。我们通过HPLC和质谱证明，用[C-13（6）]pABA或[C-13（6）] 4 HB孵育的酵母产生C-13（6）-脱甲氧基-Q（DMQ）（一种后期Q生物合成中间体）以及最终产物C-13（6）-辅酶Q。脉冲标记分析表明，异戊烯基-pABA的形成发生在几分钟内，并先于Q的合成。利用pABA作为环前体的酵母产生另一种含氮中间体4-亚氨基-DMQ（6）。该中间体在标准培养基中培养的野生型酵母和补充有pABA的abz 1突变体中少量产生。我们提出了一种机制，其中席夫碱介导的脱亚胺形成DMQ（6）醌，从而消除由pABA贡献的氮。该方案导致真核生物Q生物合成中4 HB和pABA途径的收敛，并对基于pABA的抗叶酸剂的作用产生影响。
Coenzyme Q (ubiquinone or Q) is a crucial mitochondrial lipid required for respiratory electron transport in eukaryotes. 4-Hydroxybenozoate (4HB) is an aromatic ring precursor that forms the benzoquinone ring of Q and is used extensively to examine Q biosynthesis. However, the direct precursor compounds and enzymatic steps for synthesis of 4HB in yeast are unknown. Here we show that para-aminobenzoic acid (pABA), a well known precursor of folate, also functions as a precursor for Q biosynthesis. A hexaprenylated form of pABA (prenyl-pABA) is normally present in wild-type yeast crude lipid extracts but is absent in yeast abz1 mutants starved for pABA. A stable C-13(6)-isotope of pABA (p-amino[aromatic-C-13(6)]benzoic acid ([C-13(6)]pABA)), is prenylated in either wild-type or abz1 mutant yeast to form prenyl-[C-13(6)]pABA. We demonstrate by HPLC and mass spectrometry that yeast incubated with either [C-13(6)]pABA or [C-13(6)]4HB generate both C-13(6)-demethoxy-Q (DMQ), a late stage Q biosynthetic intermediate, as well as the final product C-13(6)-coenzyme Q. Pulse-labeling analyses show that formation of prenyl-pABA occurs within minutes and precedes the synthesis of Q. Yeast utilizing pABA as a ring precursor produce another nitrogen containing intermediate, 4-imino-DMQ(6). This intermediate is produced in small quantities in wildtype yeast cultured in standard media and in abz1 mutants supplemented with pABA. We suggest a mechanism where Schiff base-mediated deimination forms DMQ(6) quinone, thereby eliminating the nitrogen contributed by pABA. This scheme results in the convergence of the 4HB and pABA pathways in eukaryotic Q biosynthesis and has implications regarding the action of pABA-based antifolates.