Italian Institute of Technology, Genoa, Italy.
Center for Genomic Sciences, Universidad National Autonoma de Mexico Campus of Cuernavaca, Cuernavaca, Morelos, Mexico.
Genome Biol Evol. 2017 Nov 1;9(11):3039-3053. doi: 10.1093/gbe/evx225.
Ubiquinone (Q) is an isoprenoid quinone that functions as membrane electron carrier in mitochondria and bacterial organisms belonging to the alpha, beta, and gamma class of proteobacteria. The biosynthesis of Q follows various biochemical steps catalyzed by diverse proteins that are, in general, homologous in mitochondria and bacteria. Nonorthologous proteins can also contribute to some biochemical steps as originally uncovered in Escherichia coli, which is the best studied organism for Q biosynthesis in prokaryotes. However, the origin of the biosynthetic pathway of Q has remained obscure. Here, I show by genome analysis that Q biosynthesis originated in cyanobacteria and then diversified in anaerobic alpha proteobacteria which have extant relatives in members of the Rhodospirillaceae family. Two distinct biochemical pathways diverged when ambient oxygen reached current levels on earth, one leading to the well-known series of Ubi genes found in E. coli, and the other containing CoQ proteins originally found in eukaryotes. Extant alpha proteobacteria show Q biosynthesis pathways that are more similar to that present in mitochondria than to that of E. coli. Hence, this work clarifies not only the origin but also the evolution of Q biosynthesis from bacteria to mitochondria.
泛醌（Q）是一种异戊二烯醌，作为线粒体和属于α、β和γ类变形杆菌的细菌的膜电子载体发挥作用。Q 的生物合成遵循各种生化步骤，这些步骤由不同的蛋白质催化，这些蛋白质在一般情况下在线粒体和细菌中是同源的。非同源蛋白也可以为一些生化步骤做出贡献，这最初是在大肠杆菌中发现的，大肠杆菌是研究原核生物 Q 生物合成的最佳生物体。然而，Q 生物合成途径的起源仍然不清楚。在这里，我通过基因组分析表明，Q 的生物合成起源于蓝细菌，然后在厌氧的α变形菌中多样化，这些细菌在红螺菌科的成员中仍有现存的亲缘关系。当环境中的氧气达到目前地球上的水平时，两个不同的生化途径发生了分歧，一个途径导致了在大肠杆菌中发现的众所周知的一系列 ubi 基因，另一个途径包含了最初在真核生物中发现的 CoQ 蛋白。现存的α变形菌显示出的 Q 生物合成途径与大肠杆菌中的途径更相似，而与线粒体中的途径不相似。因此，这项工作不仅阐明了 Q 生物合成从细菌到线粒体的起源，还阐明了它的进化。
