Minguet Eugenio G, Vera-Sirera Francisco, Marina Alberto, Carbonell Juan, Blázquez Miguel A
Instituto de Biología Molecular y Celular de Plantas (UPV-Consejo Superior de Investigaciones Científicas), Universidad Politécnica de Valencia, Valencia, Spain.
Mol Biol Evol. 2008 Oct;25(10):2119-28. doi: 10.1093/molbev/msn161. Epub 2008 Jul 24.
Polyamine biosynthesis is an ancient metabolic pathway present in all organisms. Aminopropyltransferases are key enzymes that mediate the synthesis of spermidine, spermine, and thermospermine. The relatively high sequence similarity between aminopropyltransferases and their similarity with putrescine N-methyltransferases (PMT) raises the question of whether they share a common ancestor or have evolved by convergence. Here we show that aminopropyltransferases and PMT are phylogenetically interconnected, and the different activities have been generated by unusually frequent events of diversification of existing functions. Although all spermidine synthases (SPDSs) derive from a common ancestor preceding the separation between prokaryotes and eukaryotes, they have been the origin of a variety of new activities. Among those, spermine synthases (SPMSs) represent a novelty independently arisen at least 3 times, in animals, fungi, and plants. The most parsimonious mechanism would involve the duplication and change of function of preexisting SPDS genes in each phylum. Although spermine is not essential for life, the repeated invention of SPMS and its conservation strongly argues for an evolutionary advantage derived from its presence. Moreover, the appearance of thermospermine synthase (tSPMS) in several genera of Archaea and Bacteria was accompanied by a loss of SPDS, suggesting that the new activity originated as a change of function of this enzyme. Surprisingly, tSPMS was later acquired by plants at an early stage of evolution by horizontal gene transfer and has proven to be essential for vascular development in tracheophytes. Finally, the synthesis of nicotine and tropane alkaloids in Solanales was favored by the origination of a new activity, PMT, as a duplication and change of function from SPDS.
多胺生物合成是所有生物中都存在的古老代谢途径。氨丙基转移酶是介导亚精胺、精胺和热精胺合成的关键酶。氨丙基转移酶之间相对较高的序列相似性以及它们与腐胺N -甲基转移酶（PMT）的相似性，引发了它们是否有共同祖先或是否通过趋同进化而来的问题。在这里，我们表明氨丙基转移酶和PMT在系统发育上是相互关联的，并且不同的活性是由现有功能异常频繁的多样化事件产生的。尽管所有亚精胺合酶（SPDS）都起源于原核生物和真核生物分离之前共同的祖先，但它们却成为了多种新活性的起源。其中，精胺合酶（SPMS）代表了至少在动物、真菌和植物中独立出现过3次的新事物。最简约的机制可能涉及每个门中现有SPDS基因的复制和功能变化。尽管精胺并非生命所必需，但SPMS的反复出现及其保守性有力地证明了其存在所带来的进化优势。此外，热精胺合酶（tSPMS）在古细菌和细菌的几个属中的出现伴随着SPDS的丧失，这表明这种新活性起源于该酶功能的改变。令人惊讶的是，tSPMS后来在进化早期通过水平基因转移被植物获得，并且已被证明对维管植物的维管发育至关重要。最后，茄目植物中尼古丁和托烷生物碱的合成得益于一种新活性PMT的产生，它是由SPDS复制和功能改变而来。
