Department of Microbiology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, USA.
Department of Microbiology, Blavatnik Institute, Harvard Medical School, Boston, Massachusetts, USA
mBio. 2019 Apr 16;10(2):e00194-19. doi: 10.1128/mBio.00194-19.
Biogenesis of the outer membrane of Gram-negative bacteria depends on dedicated macromolecular transport systems. The LolABCDE proteins make up the machinery for lipoprotein trafficking from the inner membrane (IM) across the periplasm to the outer membrane (OM). The Lol apparatus is additionally responsible for differentiating OM lipoproteins from those for the IM. In , a default sorting mechanism has been proposed whereby an aspartic acid at position +2 of the mature lipoproteins prevents Lol recognition and leads to their IM retention. In other bacteria, the conservation of sequences immediately following the acylated cysteine is variable. Here we show that in , the three essential Lol proteins (LolCDE) can be replaced with those from The lipoproteins MexA, OprM, PscJ, and FlgH, with different sequences at their N termini, were correctly sorted by either the or LolCDE. We further demonstrate that an inhibitor of LolCDE is active against only when expressing the orthologues. Our work shows that Lol proteins recognize a wide range of signals, consisting of an acylated cysteine and a specific conformation of the adjacent domain, determining IM retention or transport to the OM. Gram-negative bacteria build their outer membranes (OM) from components that are initially located in the inner membrane (IM). A fraction of lipoproteins is transferred to the OM by the transport machinery consisting of LolABCDE proteins. Our work demonstrates that the LolCDE complexes of the transport pathways of and are interchangeable, with the orthologues correctly sorting the lipoproteins while retaining their sensitivity to a small-molecule inhibitor. These findings question the nature of IM retention signals, identified in as aspartate at position +2 of mature lipoproteins. We propose an alternative model for the sorting of IM and OM lipoproteins based on their relative affinities for the IM and the ability of the promiscuous sorting machinery to deliver lipoproteins to their functional sites in the OM.
革兰氏阴性细菌外膜的生物发生依赖于专门的大分子运输系统。LolABCDE 蛋白构成了从内膜 (IM) 穿过周质到外膜 (OM) 运输脂蛋白的机制。Lol 装置还负责区分 OM 脂蛋白和 IM 脂蛋白。在 中，提出了一种默认的分拣机制，即成熟脂蛋白位置+2 的天冬氨酸阻止 Lol 的识别，并导致它们在 IM 中的保留。在其他细菌中，酰化半胱氨酸后面的序列的保守性是可变的。在这里，我们表明在 中，三个必需的 Lol 蛋白（LolCDE）可以被 中的那些替代。具有不同 N 末端序列的脂蛋白 MexA、OprM、PscJ 和 FlgH 通过 或 中的 LolCDE 正确分拣。我们进一步证明，抑制 LolCDE 的抑制剂在表达 同源物时仅对 有效。我们的工作表明，Lol 蛋白识别广泛的信号，包括酰化半胱氨酸和相邻结构域的特定构象，决定了 IM 的保留或转运到 OM。革兰氏阴性细菌从最初位于内膜 (IM) 的成分中构建它们的外膜 (OM)。一部分脂蛋白通过由 LolABCDE 蛋白组成的运输机制转移到 OM。我们的工作表明， 和 运输途径的 LolCDE 复合物是可互换的， 同源物正确分拣 脂蛋白，同时保留它们对小分子抑制剂的敏感性。这些发现质疑了在 中确定的 IM 保留信号的性质，即成熟脂蛋白位置+2 的天冬氨酸。我们提出了一种基于相对亲和力的 IM 和 OM 脂蛋白分拣的替代模型，以及混杂分拣机制将脂蛋白递送至 OM 中其功能部位的能力。
