Molecular Cryo-Electron Microscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, Japan.
Department of Life Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima, Japan.
Nat Struct Mol Biol. 2019 Oct;26(10):941-945. doi: 10.1038/s41594-019-0301-3. Epub 2019 Sep 30.
Bacterial locomotion by rotating flagella is achieved through the hook, which transmits torque from the motor to the filament. The hook is a tubular structure composed of a single type of protein, yet it adopts a curved shape. To perform its function, it must be simultaneously flexible and torsionally rigid. The molecular mechanism by which chemically identical subunits form such a dynamic structure is unknown. Here, we show the complete structure of the hook from Salmonella enterica in its supercoiled 'curved' state, at 2.9 Å resolution. Subunits in the curved hook are grouped into 11 distinctive conformations, each shared along 11 protofilaments. The domains of the elongated hook subunit behave as rigid bodies connected by two hinge regions. The reconstituted model demonstrates how identical subunits can dynamically change conformation by physical interactions while bending. These multiple subunit states contradict the two-state model, which is a key feature of flagellar polymorphism.
细菌通过旋转鞭毛进行运动是通过鞭毛钩实现的，鞭毛钩将力矩从发动机传递到丝状体。鞭毛钩是一种由单一类型的蛋白质组成的管状结构，但它采用了弯曲的形状。为了发挥其功能，它必须同时具有柔韧性和扭转刚性。化学性质相同的亚基如何形成这种动态结构的分子机制尚不清楚。在这里，我们以 2.9Å 的分辨率展示了弯曲状态下来自沙门氏菌的完整钩状结构。弯曲钩中的亚基被分为 11 个独特的构象，每个构象在 11 条原丝体上共享。拉长的钩状亚基的结构域表现为刚性体，通过两个铰链区连接。重建的模型演示了相同的亚基如何通过物理相互作用在弯曲的同时动态改变构象。这些多个亚基状态与二态模型相矛盾，二态模型是鞭毛多态性的关键特征。
