Department of Biological Sciences, KAIST Institute for the Biocentury, Korea Advanced Institute of Science and Technology, Daejeon 34141, Korea.
Department of Physics, Pohang University of Science and Technology, Pohang, Kyungbuk 37673, Korea.
Nat Microbiol. 2017 Jul 17;2:17114. doi: 10.1038/nmicrobiol.2017.114.
Many bacteria, including Legionella pneumophila, rely on the type IV secretion system to translocate a repertoire of effector proteins into the hosts for their survival and growth. Type IV coupling protein (T4CP) is a hexameric ATPase that links translocating substrates to the transenvelope secretion conduit. Yet, how a large number of effector proteins are selectively recruited and processed by T4CPs remains enigmatic. DotL, the T4CP of L. pneumophila, contains an ATPase domain and a C-terminal extension whose function is unknown. Unlike T4CPs involved in plasmid DNA translocation, DotL appeared to function by forming a multiprotein complex with four other proteins. Here, we show that the C-terminal extension of DotL interacts with DotN, IcmS, IcmW and an additionally identified subunit LvgA, and that this pentameric assembly binds Legionella effector proteins. We determined the crystal structure of this assembly and built an architecture of the T4CP holocomplex by combining a homology model of the ATPase domain of DotL. The holocomplex is a hexamer of a bipartite structure composed of a membrane-proximal ATPase domain and a membrane-distal substrate-recognition assembly. The presented information demonstrates the architecture and functional dissection of the multiprotein T4CP complexes and provides important insights into their substrate recruitment and processing.
许多细菌，包括嗜肺军团菌，依赖于 IV 型分泌系统将一系列效应蛋白转运到宿主细胞中，以维持其生存和生长。IV 型偶联蛋白（T4CP）是一种六聚体 ATP 酶，可将转运底物与跨膜分泌导管连接起来。然而，大量效应蛋白如何被 T4CPs 选择性招募和加工仍然是一个谜。嗜肺军团菌的 T4CP DotL 包含一个 ATP 酶结构域和一个 C 端延伸结构域，其功能尚不清楚。与参与质粒 DNA 转运的 T4CP 不同，DotL 似乎通过与其他四种蛋白质形成多蛋白复合物来发挥作用。在这里，我们表明 DotL 的 C 端延伸与 DotN、IcmS、IcmW 和另外鉴定的亚基 LvgA 相互作用，并且这个五聚体组装物结合 Legionella 效应蛋白。我们确定了这个组装物的晶体结构，并通过结合 DotL 的 ATP 酶结构域的同源模型构建了 T4CP 全复合物的结构。全复合物是由膜近端 ATP 酶结构域和膜远端底物识别组装体组成的二聚体结构的六聚体。所提供的信息展示了多蛋白 T4CP 复合物的结构和功能剖析，并为它们的底物招募和加工提供了重要的见解。
