Function and structure of novel glycolipid essential for membrane protein integration

我们在大肠杆菌的内膜中发现了一种新的整合因子，命名为MPIase（膜蛋白整合酶）。MPIase原来是一种糖脂，由二酰基甘油和通过焦磷酸连接的三个乙酰化氨基糖的聚糖链组成。水解去除脂质部分得到的可溶性产物比原始的MPIase具有更高的整合活性。这种可溶形式的MPIase直接与新生膜蛋白相互作用，维持其整合能力结构，并允许其在翻译后整合到膜中。因此，mpase对膜蛋白具有整合专用的伴侣蛋白样活性

We have found a novel integration factor in the inner membrane of E. coli, naming it MPIase (membrane protein integrase). MPIase turned out to be a glycolipid composed of diacylglycerol and a glycan chain of three acetylated aminosugars linked through pyrophosphate. Hydrolytic removal of the lipid moiety gave a soluble product with higher integration activity than that of the original MPIase. This soluble form of MPIase directly interacts with a newborn membrane protein, maintaining its integration-competent structure, and allowing its post-translational integration into membranes. Thus, MPIase possesses integration-dedicated chaperone-like activity toward membrane proteins