Archaea-type ether lipids in Bacteria: biosynthesis, processing, and physiological function

乙醚类脂是由带有聚戊烯基侧链的sn-甘油-1-磷酸(G1P)支架组成的，仅在古生代中被发现，因此被认为是这一系统发育领域的标志。最近，我们通过证明聚戊烯基甘油磷酸合成酶PcrB催化枯草杆菌和相关领域细菌的革兰氏阳性物种合成基于G1P的乙醚脂质七烯基甘油基磷酸(HepGP)，证明了这一范式是错误的。我们进一步证明了HepGP在体内是通过去磷酸化和乙酰化来处理的。由于以前没有观察到任何乙醚类脂类的这种修饰，我们将提纯和鉴定涉及的磷酸酶和乙酰转移酶。此外，我们计划通过分析不同的枯草杆菌敲除菌株的生长表型和膜组成，并与野生型细胞进行比较，来阐明新型细菌醚脂的生物学功能。在数据库搜索中，我们在细菌中发现了第二组聚戊烯基甘油磷酸合成酶，这些合成酶仅在革兰氏阴性物种中发现，其序列与PcrB有很大差异。我们将鉴定这组未知酶的聚戊烯基底物和醚脂产物，并阐明细菌聚戊烯基甘油磷酸合成酶与古生菌的底物特异性的结构基础。我们的研究将对细菌中乙醚类脂的生物合成和生理功能提供全面的了解。

Ether lipids consisting of a sn-glycerol-1-phosphate (G1P) scaffold with attached polyprenyl side chains have been found exclusively within the Archaea and have therefore been considered a hallmark of this phylogenetic domain. We have recently disproved this paradigm by showing that the polyprenylglyceryl phosphate synthase PcrB catalyzes the synthesis of the G1P-based ether lipid heptaprenylglyceryl phosphate (HepGP) in Bacillus subtilis and related Gram-positive species from the domain Bacteria. We have further demonstrated that HepGP is processed in vivo by dephosphorylation and acetylation. Since such modifications have previously not been observed for any ether lipid, we will purify and characterize the involved phosphatase and acetyltransferase enzymes. Moreover, we plan to elucidate the biological function of the novel bacterial ether lipids by analyzing the growth phenotype and membrane composition of various B. subtilis knock-out strains in comparison with wild-type cells. In a database search we have identified a second group of polyprenylglyceryl phosphate synthases in Bacteria, which are found exclusively in Gram-negative species and whose sequences differ considerably from PcrB. We will identify the polyprenyl substrate and the ether lipid product of this uncharacterized group of enzymes and elucidate the structural basis for the substrate specificities of polyprenylglyceryl phosphate synthases from Bacteria in comparison to those of Archaea. Our studies shall provide a comprehensive understanding of the biosynthesis and physiological function of ether lipids in Bacteria.