Three classes of ion-driven protein motors have been identified to date: ATP synthase, the bacterial flagellar motor and a proton-driven motor that powers gliding motility and the type 9 protein secretion system in Bacteroidetes bacteria. Here, we present cryo-electron microscopy structures of the gliding motility/type 9 protein secretion system motors GldLM from Flavobacterium johnsoniae and PorLM from Porphyromonas gingivalis. The motor is an asymmetric inner membrane protein complex in which the single transmembrane helices of two periplasm-spanning GldM/PorM proteins are positioned inside a ring of five GldL/PorL proteins. Mutagenesis and single-molecule tracking identify protonatable amino acid residues in the transmembrane domain of the complex that are important for motor function. Our data provide evidence for a mechanism in which proton flow results in rotation of the periplasm-spanning GldM/PorM dimer inside the intra-membrane GldL/PorL ring to drive processes at the bacterial outer membrane.

迄今为止，已鉴定出三类离子驱动的蛋白质马达：ATP 合酶、细菌鞭毛马达和为拟杆菌中的滑行运动和 9 型蛋白质分泌系统提供动力的质子驱动马达。在这里，我们展示了来自约氏黄杆菌的滑动运动/9型蛋白分泌系统马达GldLM和来自牙龈卟啉单胞菌的PorLM的冷冻电子显微镜结构。马达是一种不对称内膜蛋白复合物，其中两个跨周质的 GldM/PorM 蛋白的单跨膜螺旋位于五个 GldL/PorL 蛋白的环内。诱变和单分子追踪识别了复合物跨膜结构域中对运动功能重要的可质子化氨基酸残基。我们的数据为质子流导致膜内 GldL/PorL 环内跨周质的 GldM/PorM 二聚体旋转以驱动细菌外膜的过程提供了证据。