The divergence of archaea, bacteria and eukaryotes was a fundamental step in evolution. One marker of this event is a major difference in membrane lipid chemistry between these kingdoms. Whereas the membranes of bacteria and eukaryotes primarily consist of straight fatty acids ester-bonded to glycerol-3-phosphate, archaeal phospholipids consist of isoprenoid chains ether-bonded to glycerol-1-phosphate. Notably, the mechanisms underlying the biosynthesis of these lipids remain elusive. Here, we report the structure of the CDP-archaeol synthase (CarS) of Aeropyrum pernix (ApCarS) in the CTP- and Mg2+-bound state at a resolution of 2.4 Å. The enzyme comprises a transmembrane domain with five helices and cytoplasmic loops that together form a large charged cavity providing a binding site for CTP. Identification of the binding location of CTP and Mg2+ enabled modeling of the specific lipophilic substrate-binding site, which was supported by site-directed mutagenesis, substrate-binding affinity analyses, and enzyme assays. We propose that archaeol binds within two hydrophobic membrane-embedded grooves formed by the flexible transmembrane helix 5 (TM5), together with TM1 and TM4. Collectively, structural comparisons and analyses, combined with functional studies, not only elucidated the mechanism governing the biosynthesis of phospholipids with ether-bonded isoprenoid chains by CTP transferase, but also provided insights into the evolution of this enzyme superfamily from archaea to bacteria and eukaryotes.


中文翻译：

---

膜中CDP-古生物合成的结构和机理研究

古细菌，细菌和真核生物的分化是进化的基本步骤。此事件的一个标志是这些王国之间膜脂质化学的主要差异。细菌和真核生物的膜主要由酯键合至3-磷酸甘油酯的直链脂肪酸组成，而古细菌磷脂由醚键合至1-磷酸甘油酯的类异戊二烯链组成。值得注意的是，这些脂质生物合成的基础机制仍然难以捉摸。在这里，我们报道了CTP-和Mg2 +-结合状态的Ceropyrum pernix（ApCarS）CDP-archaeol合酶（CarS）的结构，其分辨率为2.4。该酶包含具有五个螺旋和胞质环的跨膜结构域，这些螺旋和胞质环一起形成了一个大的带电荷的腔，为CTP提供了结合位点。CTP和Mg2 +结合位点的鉴定使得能够对特定亲脂性底物结合位点进行建模，这由定点诱变，底物结合亲和力分析和酶分析支持。我们建议古细菌在由柔性跨膜螺旋5（TM5）以及TM1和TM4形成的两个疏水膜嵌入凹槽中结合。总体上，结构比较和分析，结合功能研究，不仅阐明了通过CTP转移酶控制具有醚键合类异戊二烯链的磷脂生物合成的机制，而且还提供了对该酶超家族从古细菌到细菌和真核生物进化的见解。底物结合亲和力分析和酶分析。我们建议古细菌在由柔性跨膜螺旋5（TM5）以及TM1和TM4形成的两个疏水膜嵌入凹槽内结合。总体上，结构比较和分析，结合功能研究，不仅阐明了通过CTP转移酶控制具有醚键合类异戊二烯链的磷脂生物合成的机制，而且还提供了对该酶超家族从古细菌到细菌和真核生物进化的见解。底物结合亲和力分析和酶分析。我们建议古细菌在由柔性跨膜螺旋5（TM5）以及TM1和TM4形成的两个疏水膜嵌入凹槽中结合。总体上，结构比较和分析，结合功能研究，不仅阐明了通过CTP转移酶控制具有醚键合类异戊二烯链的磷脂生物合成的机制，而且还提供了对该酶超家族从古细菌到细菌和真核生物进化的见解。