Department of Cell Biology, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA.
Department of Cell Biology, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA; Applied Bioinformatics Laboratories, New York University School of Medicine, New York, NY, USA.
Cell. 2020 Apr 30;181(3):653-664.e19. doi: 10.1016/j.cell.2020.03.030.
Gram-negative bacteria are surrounded by an outer membrane composed of phospholipids and lipopolysaccharide, which acts as a barrier and contributes to antibiotic resistance. The systems that mediate phospholipid trafficking across the periplasm, such as MCE (Mammalian Cell Entry) transporters, have not been well characterized. Our ~3.5 Å cryo-EM structure of the E. coli MCE protein LetB reveals an ~0.6 megadalton complex that consists of seven stacked rings, with a central hydrophobic tunnel sufficiently long to span the periplasm. Lipids bind inside the tunnel, suggesting that it functions as a pathway for lipid transport. Cryo-EM structures in the open and closed states reveal a dynamic tunnel lining, with implications for gating or substrate translocation. Our results support a model in which LetB establishes a physical link between the two membranes and creates a hydrophobic pathway for the translocation of lipids across the periplasm.
革兰氏阴性菌的外膜由磷脂和脂多糖组成，充当屏障并有助于抗生素耐药性的产生。介导磷脂在周质中运输的系统，如哺乳动物细胞进入（MCE）转运蛋白，尚未得到很好的描述。我们约 3.5Å 的大肠杆菌 MCE 蛋白 LetB 的冷冻电镜结构揭示了一个约 0.6 兆道尔顿的复合物，由七个堆叠的环组成，其中央的疏水性隧道足够长，可以跨越周质。脂质结合在隧道内，表明其作为脂质运输途径发挥作用。开放和关闭状态的冷冻电镜结构揭示了一个动态的隧道衬里，这对门控或底物易位有影响。我们的结果支持了这样一种模型，即 LetB 在两个膜之间建立了物理连接，并为脂质穿过周质的易位创建了疏水途径。
