Data from: Structure of FlgK reveals the divergence of the bacterial hook-filament junction of Campylobacter

Evolution of a nano-machine consisting of multiple parts, each with a specific function, is a complex process. A change in one part should eventually result in changes in other parts, if the overall function is to be conserved. In bacterial flagella, the filament and the hook have distinct functions and their respective proteins, FliC and FlgE, have different three-dimensional structures. The filament functions as a helical propeller and the hook as a flexible universal joint. Two proteins, FlgK and FlgL, assure a smooth connectivity between the hook and the filament. Here we show that, in Campylobacter, the 3D structure of FlgK differs from that of its orthologs in Salmonella and Burkholderia, whose structures have previously been solved. Docking the model of the FlgK junction onto the structure of the Campylobacter hook provides some clues about its divergence. These data suggest how evolutionary pressure to adapt to structural constraints, due to the structure of Campylobacter hook, causes divergence of one element of a supra-molecular complex in order to maintain the function of the entire flagellar assembly.

由多个具备特定功能的部件组成的纳米机器，其演化过程极为复杂。若要维持整体功能，某一部件的改变最终必然会引发其他部件的相应变化。在细菌鞭毛（bacterial flagella）中，丝状体（filament）与钩形鞘（hook）功能迥异，其对应的蛋白质FliC与FlgE的三维结构亦不相同：丝状体作为螺旋推进器发挥作用，钩形鞘则充当柔性万向节。两种蛋白质FlgK与FlgL负责保障钩形鞘与丝状体之间的平稳连接。本研究显示，在弯曲杆菌（Campylobacter）中，FlgK的三维结构与其在沙门氏菌（Salmonella）和伯克霍尔德菌（Burkholderia）中的直系同源蛋白存在差异，后两者的结构此前已被解析。将FlgK连接区的模型分子对接至弯曲杆菌钩形鞘的结构中，可为其演化分化提供若干线索。这些数据揭示了：由于弯曲杆菌钩形鞘的结构特性，为适应结构约束而产生的演化压力，如何促使超分子复合物（supra-molecular complex）的某一组分发生分化，以维持整个鞭毛组装体的功能。