Structural and mechanistic insights into the biosynthesis of CDP-archaeol in membranes

• 来源期刊: 细胞研究（英文版）
• 年，卷（期）: 2017,（11）
• 页码范围: 1378-1391
• 页数: 14页
• 语种: 英文
• DOI: 10.1038/cr.2017.122

摘要

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 (A).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.