Chng Shu-Sin, Xue Mingyu, Garner Ronald A, Kadokura Hiroshi, Boyd Dana, Beckwith Jonathan, Kahne Daniel
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
Science. 2012 Sep 28;337(6102):1665-8. doi: 10.1126/science.1227215. Epub 2012 Aug 30.
The presence of lipopolysaccharide (LPS) on the cell surface of Gram-negative bacteria is critical for viability. A conserved β-barrel membrane protein LptD (lipopolysaccharide transport protein D) translocates LPS from the periplasm across the outer membrane (OM). In Escherichia coli, this protein contains two disulfide bonds and forms the OM LPS translocon with the lipoprotein LptE. Here, we identified seven in vivo states on the oxidative-folding pathway of LptD. Proper assembly involved a nonfunctional intermediate containing non-native disulfides. Intermediate formation required the oxidase DsbA, and subsequent maturation to the active form with native disulfides was triggered by LptE. Thus, disulfide bond-dependent protein folding of LptD requires the proper assembly of a two-protein complex to promote disulfide bond rearrangement.
革兰氏阴性菌细胞表面脂多糖（LPS）的存在对其生存能力至关重要。一种保守的β-桶状膜蛋白LptD（脂多糖转运蛋白D）将LPS从周质转运穿过外膜（OM）。在大肠杆菌中，该蛋白含有两个二硫键，并与脂蛋白LptE形成外膜LPS转运体。在此，我们确定了LptD氧化折叠途径上的七种体内状态。正确组装涉及一个含有非天然二硫键的无功能中间体。中间体的形成需要氧化酶DsbA，随后由LptE触发其成熟为具有天然二硫键的活性形式。因此，LptD的二硫键依赖性蛋白折叠需要一个双蛋白复合物的正确组装来促进二硫键重排。
