Department of Chemistry and Singapore Center for Environmental Life Sciences Engineering, National University of Singapore, Singapore; email:
Annu Rev Microbiol. 2024 Nov;78(1):553-573. doi: 10.1146/annurev-micro-032521-014507. Epub 2024 Nov 7.
Gram-negative bacteria build an asymmetric outer membrane (OM), with lipopolysaccharides (LPS) and phospholipids (PLs) occupying the outer and inner leaflets, respectively. This distinct lipid arrangement is widely conserved within the Bacteria domain and confers strong protection against physical and chemical insults. The OM is physically separated from the inner membrane and the cytoplasm, where most cellular resources are located; therefore, the cell faces unique challenges in the assembly and maintenance of this asymmetric bilayer. Here, we present a framework for how gram-negative bacteria initially establish and continuously maintain OM lipid asymmetry, discussing the state-of-the-art knowledge of specialized lipid transport machines that place LPS and PLs directly into their corresponding leaflets in the OM, prevent excess PL accumulation and mislocalization, and correct any lipid asymmetry defects. We critically assess current studies, or the lack thereof, and highlight important future directions for research on OM lipid transport, homeostasis, and asymmetry.
革兰氏阴性菌构建了不对称的外膜（OM），其中脂多糖（LPS）和磷脂（PLs）分别占据外膜和内膜小叶。这种独特的脂质排列在细菌域中广泛保守，并赋予了对物理和化学损伤的强大保护。OM 与内膜和细胞质物理上分离，而细胞质中包含了大多数细胞资源；因此，细胞在组装和维持这种不对称双层膜时面临着独特的挑战。在这里，我们提出了一个框架，说明革兰氏阴性菌如何最初建立并持续维持 OM 脂质不对称性，讨论了专门的脂质转运机制的最新知识，这些机制将 LPS 和 PL 直接放置在 OM 的相应小叶中，防止 PL 过度积累和定位错误，并纠正任何脂质不对称缺陷。我们批判性地评估了当前的研究，或缺乏研究，并强调了关于 OM 脂质转运、动态平衡和不对称性的研究的重要未来方向。
