PDF(Pubmed)
Abstract：
Biosynthesis of sterols, which are key constituents of canonical eukaryotic membranes, requires molecular oxygen. Anaerobic protists and deep-branching anaerobic fungi are the only eukaryotes in which a mechanism for sterol-independent growth has been elucidated. In these organisms, tetrahymanol, formed through oxygen-independent cyclization of squalene by a squalene-tetrahymanol cyclase, acts as a sterol surrogate. This study confirms an early report [C. J. E. A. Bulder, Antonie Van Leeuwenhoek, 37, 353-358 (1971)] that Schizosaccharomyces japonicus is exceptional among yeasts in growing anaerobically on synthetic media lacking sterols and unsaturated fatty acids. Mass spectrometry of lipid fractions of anaerobically grown Sch. japonicus showed the presence of hopanoids, a class of cyclic triterpenoids not previously detected in yeasts, including hop-22(29)-ene, hop-17(21)-ene, hop-21(22)-ene, and hopan-22-ol. A putative gene in Sch. japonicus showed high similarity to bacterial squalene-hopene cyclase (SHC) genes and in particular to those of Acetobacter species. No orthologs of the putative Sch. japonicus SHC were found in other yeast species. Expression of the Sch. japonicus SHC gene (Sjshc1) in Saccharomyces cerevisiae enabled hopanoid synthesis and stimulated anaerobic growth in sterol-free media, thus indicating that one or more of the hopanoids produced by SjShc1 could at least partially replace sterols. Use of hopanoids as sterol surrogates represents a previously unknown adaptation of eukaryotic cells to anaerobic growth. The fast anaerobic growth of Sch. japonicus in sterol-free media is an interesting trait for developing robust fungal cell factories for application in anaerobic industrial processes.
摘要：
甾醇的生物合成，它们是经典真核细胞膜的关键成分，需要分子氧。厌氧原生生物和深分支厌氧真菌是唯一阐明了不依赖固醇生长机制的真核生物。在这些生物中，四烯醇,通过角鲨烯-四氢酚环化酶使角鲨烯不依赖氧的环化形成，充当固醇替代品。这项研究证实了早期报告[C.J.E.A.Bulder,安东尼·范·列文虎克，37，353-358（1971）]在缺乏固醇和不饱和脂肪酸的合成培养基上厌氧生长的酵母中，日本裂殖酵母是例外。厌氧生长的Sch的脂质部分的质谱。日本刺血鱼显示出了类大麻的存在，一类以前在酵母中检测不到的环状三萜类化合物，包括Hop-22(29)-ene，跳-17(21)-烯,跳-21(22)-烯,和Hopan-22-ol.Sch中的推定基因。japonicus与细菌角鲨烯-hopene环化酶（SHC）基因，特别是与醋杆菌属物种的相似性很高。没有推定的Sch的直系同源物。在其他酵母物种中发现了日本刺槐SHC。Sch的表达。酿酒酵母中的japonicusSHC基因（Sjshc1）能够在无甾醇的培养基中进行类hopanoid合成并刺激厌氧生长，因此表明一种或多种由SjShc1产生的类植物可以至少部分替代固醇。使用类hopanoid作为固醇替代物代表了真核细胞对厌氧生长的先前未知的适应。Sch的快速厌氧生长。在无固醇培养基中的日本花是开发用于厌氧工业过程的强大真菌细胞工厂的有趣特征。
