Université Grenoble Alpes, Institut de Biologie Structurale, 71 avenue des Martyrs - CS10090, 38044, Grenoble cedex 9, France.
CEA, DSV, Institut de Biologie Structurale, 71 avenue des Martyrs - CS10090, 38044, Grenoble cedex 9, France.
Sci Rep. 2017 Aug 29;7(1):9715. doi: 10.1038/s41598-017-10136-0.
Transport of lipopolysaccharides (LPS) to the surface of the outer membrane is essential for viability of Gram-negative bacteria. Periplasmic LptC and LptA proteins of the LPS transport system (Lpt) are responsible for LPS transfer between the Lpt inner and outer membrane complexes. Here, using a monomeric E. coli LptA mutant, we first show in vivo that a stable LptA oligomeric form is not strictly essential for bacteria. The LptC-LptA complex was characterized by a combination of SAXS and NMR methods and a low resolution model of the complex was determined. We were then able to observe interaction of LPS with LptC, the monomeric LptA mutant as well as with the LptC-LptA complex. A LptC-LPS complex was built based on NMR data in which the lipid moiety of the LPS is buried at the interface of the two β-jellyrolls of the LptC dimer. The selectivity of LPS for this intermolecular surface and the observation of such cavities at homo- or heteromolecular interfaces in LptC and LptA suggests that intermolecular sites are essential for binding LPS during its transport.
脂多糖（LPS）向外膜表面的转运对于革兰氏阴性细菌的存活至关重要。LPS 转运系统（Lpt）的周质 LptC 和 LptA 蛋白负责 LPS 在 Lpt 内膜和外膜复合物之间的转移。在这里，我们首次使用单体大肠杆菌 LptA 突变体在体内证明，稳定的 LptA 寡聚形式对于细菌并非严格必需的。通过 SAXS 和 NMR 方法结合的方法对 LptC-LptA 复合物进行了表征，并确定了复合物的低分辨率模型。然后，我们能够观察到 LPS 与 LptC、单体 LptA 突变体以及 LptC-LptA 复合物的相互作用。基于 NMR 数据构建了 LptC-LPS 复合物，其中 LPS 的脂质部分埋藏在 LptC 二聚体的两个β-发夹之间的界面处。这种 LPS 对这种分子间表面的选择性以及在 LptC 和 LptA 中的同或异分子界面上观察到这种腔的现象表明，在 LPS 转运过程中，分子间位点对于 LPS 的结合是必不可少的。
