In rod-shaped bacteria, type IV pili (Tfp) promote twitching motility by assembling and retracting at the cell pole. In Myxococcus xanthus, a bacterium that moves in highly coordinated cell groups, Tfp are activated by a polar activator protein, SgmX. However, while it is known that the Ras-like protein MglA is required for unipolar targeting, how SgmX accesses the cell pole to activate Tfp is unknown. Here, we demonstrate that a polar beacon protein, FrzS, recruits SgmX at the cell pole. We identified two main functional domains, including a Tfp-activating domain and a polar-binding domain. Within the latter, we show that the direct binding of MglA-GTP unveils a hidden motif that binds directly to the FrzS N-terminal response regulator (CheY). Structural analyses reveal that this binding occurs through a novel binding interface for response regulator domains. In conclusion, the findings unveil the protein interaction network leading to the spatial activation of Tfp at the cell pole. This tripartite system is at the root of complex collective behaviours in this predatory bacterium.

中文翻译：

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FrzS 作为极地灯塔招募 SgmX，Myxococcus xanthus 运动期间 IV 型菌毛的中枢激活剂

在杆状细菌中，IV 型菌毛 (Tfp) 通过在细胞极处组装和收缩来促进抽搐运动。在黄粘球菌中，一种在高度协调的细胞群中移动的细菌，Tfp 被极性激活蛋白 SgmX 激活。然而，虽然已知单极靶向需要 Ras 样蛋白 MglA，但 SgmX 如何进入细胞极以激活 Tfp 尚不清楚。在这里，我们证明极性信标蛋白 FrzS 在细胞极招募 SgmX。我们确定了两个主要功能域，包括 Tfp 激活域和极性结合域。在后者中，我们表明 MglA-GTP 的直接结合揭示了一个隐藏的基序，该基序直接结合到 FrzS N 末端响应调节器 (CheY)。结构分析表明，这种结合是通过响应调节域的新型结合界面发生的。总之，这些发现揭示了导致细胞极处 Tfp 空间激活的蛋白质相互作用网络。