The motile-sessile transition is critical for bacterial survival and growth. Cyclic-di-GMP (c-di-GMP) plays a central role in controlling this transition and regulating biofilm formation via various effectors. As an effector of c-di-GMP in Escherichia coli and related species, the PilZ domain-containing protein YcgR responds to elevated c-di-GMP concentrations and acts on the flagellar motor to suppress bacterial motility in a brakelike fashion, which promotes bacterial surface attachment. To date, several target proteins within the motor, MotA, FliG, and FliM, along with different regulatory mechanisms have been reported. However, how YcgR acts on these components remains unclear. Here, we report that activated YcgR stably binds to MotA at the MotA-FliG interface and thereby regulates bacterial swimming. Biochemical and structural analyses revealed that c-di-GMP rearranges the PilZ domain configuration, resulting in the formation of a MotA-binding patch consisting of an RXXXR motif and the C-tail helix α3. Moreover, we noted that a conserved region in the YcgR-N domain, which is independent of MotA interaction, is necessary for motility regulation. On the basis of these findings, we infer that the YcgR-N domain is required for activity on other motor proteins. We propose that activated YcgR appends to MotA via its PilZ domain and thereby interrupts the MotA-FliG interaction and simultaneously interacts with other motor proteins via its YcgR-N domain to inhibit flagellar motility. Our findings suggest that the mode of interaction between YcgR and motor proteins may be shared by other PilZ family proteins.

中文翻译：

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结构见解的c-di-GMP绑定YcgR调节大肠杆菌鞭毛运动的机制。

运动无柄过渡对于细菌存活和生长至关重要。环二GMP（c-di-GMP）在控制这种过渡和通过各种效应子调节生物膜形成中起着核心作用。作为大肠杆菌和相关物种中c-di-GMP的效应物，含有PilZ域的蛋白质YcgR对升高的c-di-GMP浓度作出反应，并以鞭毛状方式抑制鞭毛运动，从而抑制细菌运动，从而促进细菌生长。表面附着。迄今为止，已经报道了运动中的几种靶蛋白，MotA，FliG和FliM，以及不同的调节机制。但是，尚不清楚YcgR如何作用于这些组件。在这里，我们报告激活的YcgR稳定地结合MotA-FliG界面上的MotA，从而调节细菌游泳。生化和结构分析表明，c-di-GMP重排了PilZ域的结构，导致形成了由RXXXR基序和C-尾螺旋α3组成的MotA结合补丁。此外，我们注意到，YcgR-N域中一个独立于MotA相互作用的保守区域对于运动调节是必需的。基于这些发现，我们推断YcgR-N结构域是其他电机蛋白活性所必需的。我们建议激活的YcgR经由其PilZ结构域附加到MotA，从而中断MotA-FliG相互作用，并同时通过其YcgR-N结构域与其他运动蛋白相互作用，从而抑制鞭毛运动。我们的发现表明，YcgR与运动蛋白之间的相互作用方式可能与其他PilZ家族蛋白共享。