Abstract：
Carotenoids are isoprenoid lipids found across the tree of life with important implications in oxidative stress adaptations, photosynthetic metabolisms, as well as in membrane dynamics. The canonical view is that C40 carotenoids are synthesized from phytoene and C30 carotenoids from diapophytoene. Squalene is mostly associated with the biosynthesis of polycyclic triterpenes, although there have been suggestions that it could also be involved in the biosynthesis of C30 carotenoids. However, demonstration of the existence of this pathway in nature is lacking. Here, we demonstrate that C30 carotenoids are synthesized from squalene in the Planctomycetes bacteria and that this squalene route to C30 carotenoids is the most widespread in prokaryotes. Using the evolutionary history of carotenoid and squalene amino oxidases, we propose an evolutionary scenario to explain the origin and diversification of the different carotenoid and squalene-related pathways. We show that carotenoid biosynthetic pathways have been constantly transferred and neofunctionalized during prokaryotic evolution. One possible origin of the squalene pathway connects it with the one of C40 carotenoid synthesis of Cyanobacteria. The widespread occurrence of the squalene route to C30 carotenoids in Bacteria increases the functional repertoire of squalene, establishing it as a general hub of carotenoids and polycyclic triterpenes synthesis.
摘要：
类胡萝卜素是在生命之树中发现的类异戊二烯脂质，在氧化应激适应中具有重要意义。光合代谢，以及膜动力学。典型的观点是，C40类胡萝卜素是从八叶烯合成的，而C30类胡萝卜素是从二叶八叶烯合成的。角鲨烯主要与多环三萜的生物合成有关，尽管有人认为它也可能参与C30类胡萝卜素的生物合成。然而,自然界中缺乏这种途径存在的证明。这里,我们证明了C30类胡萝卜素是由Planctomycetes细菌中的角鲨烯合成的，并且这种角鲨烯通往C30类胡萝卜素的途径在原核生物中最为普遍。利用类胡萝卜素和角鲨烯氨基氧化酶的进化史，我们提出了一个进化情景来解释不同类胡萝卜素和角鲨烯相关途径的起源和多样化。我们表明类胡萝卜素生物合成途径在原核进化过程中不断转移和新功能化。角鲨烯途径的一个可能的起源将其与蓝细菌的C40类胡萝卜素合成之一联系起来。角鲨烯途径在细菌中的C30类胡萝卜素的广泛出现增加了角鲨烯的功能库，建立它作为类胡萝卜素和多环三萜合成的一般枢纽。
