Konovalova Anna, Silhavy Thomas J
Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Washington Road, Princeton, NJ 08544, USA.
Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Washington Road, Princeton, NJ 08544, USA
Philos Trans R Soc Lond B Biol Sci. 2015 Oct 5;370(1679). doi: 10.1098/rstb.2015.0030.
Bacterial lipoproteins are lipid-anchored proteins that contain acyl groups covalently attached to the N-terminal cysteine residue of the mature protein. Lipoproteins are synthesized in precursor form with an N-terminal signal sequence (SS) that targets translocation across the cytoplasmic or inner membrane (IM). Lipid modification and SS processing take place at the periplasmic face of the IM. Outer membrane (OM) lipoproteins take the localization of lipoproteins (Lol) export pathway, which ends with the insertion of the N-terminal lipid moiety into the inner leaflet of the OM. For many lipoproteins, the biogenesis pathway ends here. We provide examples of lipoproteins that adopt complex topologies in the OM that include transmembrane and surface-exposed domains. Biogenesis of such lipoproteins requires additional steps beyond the Lol pathway. In at least one case, lipoprotein sequences reach the cell surface by being threaded through the lumen of a beta-barrel protein in an assembly reaction that requires the heteropentomeric Bam complex. The inability to predict surface exposure reinforces the importance of experimental verification of lipoprotein topology and we will discuss some of the methods used to study OM protein topology.
细菌脂蛋白是脂质锚定蛋白,其含有共价连接至成熟蛋白N端半胱氨酸残基的酰基。脂蛋白以前体形式合成,带有N端信号序列(SS),该信号序列靶向跨细胞质膜或内膜(IM)的转运。脂质修饰和信号序列加工在IM的周质面进行。外膜(OM)脂蛋白采用脂蛋白(Lol)输出途径进行定位,该途径以N端脂质部分插入OM的内小叶结束。对于许多脂蛋白而言,生物合成途径到此为止。我们提供了在OM中采用复杂拓扑结构的脂蛋白实例,这些拓扑结构包括跨膜结构域和表面暴露结构域。此类脂蛋白的生物合成需要Lol途径之外的额外步骤。至少在一种情况下,脂蛋白序列通过在需要异五聚体Bam复合物的组装反应中穿过β桶蛋白的内腔到达细胞表面。无法预测表面暴露情况凸显了实验验证脂蛋白拓扑结构的重要性,我们将讨论一些用于研究OM蛋白拓扑结构的方法。