Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom.
J Biol Chem. 2010 May 7;285(19):14711-23. doi: 10.1074/jbc.M110.107219. Epub 2010 Mar 1.
Polyamines are small flexible organic polycations found in almost all cells. They likely existed in the last universal common ancestor of all extant life, and yet relatively little is understood about their biological function, especially in bacteria and archaea. Unlike eukaryotes, where the predominant polyamine is spermidine, bacteria may contain instead an alternative polyamine, sym-homospermidine. We demonstrate that homospermidine synthase (HSS) has evolved vertically, primarily in the alpha-Proteobacteria, but enzymatically active, diverse HSS orthologues have spread by horizontal gene transfer to other bacteria, bacteriophage, archaea, eukaryotes, and viruses. By expressing diverse HSS orthologues in Escherichia coli, we demonstrate in vivo the production of co-products diaminopropane and N(1)-aminobutylcadaverine, in addition to sym-homospermidine. We show that sym-homospermidine is required for normal growth of the alpha-proteobacterium Rhizobium leguminosarum. However, sym-homospermidine can be replaced, for growth restoration, by the structural analogues spermidine and sym-norspermidine, suggesting that the symmetrical or unsymmetrical form and carbon backbone length are not critical for polyamine function in growth. We found that the HSS enzyme evolved from the alternative spermidine biosynthetic pathway enzyme carboxyspermidine dehydrogenase. The structure of HSS is related to lysine metabolic enzymes, and HSS and carboxyspermidine dehydrogenase evolved from the aspartate family of pathways. Finally, we show that other bacterial phyla such as Cyanobacteria and some alpha-Proteobacteria synthesize sym-homospermidine by an HSS-independent pathway, very probably based on deoxyhypusine synthase orthologues, similar to the alternative homospermidine synthase found in some plants. Thus, bacteria can contain alternative biosynthetic pathways for both spermidine and sym-norspermidine and distinct alternative pathways for sym-homospermidine.
多胺是存在于几乎所有细胞中的小而灵活的有机聚阳离子。它们可能存在于所有现存生命的最后一个普遍共同祖先中，但人们对它们的生物学功能知之甚少，尤其是在细菌和古菌中。与真核生物中占优势的多胺是精脒不同，细菌中可能含有替代的多胺，即 sym-同型精脒。我们证明 homospermidine synthase（HSS）是垂直进化的，主要存在于α变形菌中，但具有酶活性的多样化 HSS 同源物已经通过水平基因转移传播到其他细菌、噬菌体、古菌、真核生物和病毒中。通过在大肠杆菌中表达不同的 HSS 同源物，我们在体内证明了除 sym-homospermidine 外，还产生了副产物二氨基丙垸和 N(1)-氨丁基 cadaverine。我们表明，sym-homospermidine 是α变形菌 Rhizobium leguminosarum 正常生长所必需的。然而，sym-homospermidine 可以被结构类似物 spermidine 和 sym-norspermidine 取代，以恢复生长，这表明在生长中，多胺的功能对于其对称或不对称形式和碳骨架长度并不关键。我们发现 HSS 酶是从替代的 spermidine 生物合成途径酶 carboxyspermidine dehydrogenase 进化而来的。HSS 的结构与赖氨酸代谢酶有关，HSS 和 carboxyspermidine dehydrogenase 是从天冬氨酸途径进化而来的。最后，我们表明，其他细菌门，如蓝藻和一些α变形菌，通过独立于 HSS 的途径合成 sym-homospermidine，很可能基于 deoxyhypusine synthase 同源物，类似于一些植物中发现的替代 homospermidine synthase。因此，细菌可以包含 spermidine 和 sym-norspermidine 的替代生物合成途径，以及用于 sym-homospermidine 的独特替代途径。
