Cyclic-di-guanosine monophosphate (c-di-GMP) is an important effector associated with acute-chronic infection transition in Pseudomonas aeruginosa. Previously, we reported a signaling network SiaABCD which regulates biofilm formation by modulating c-di-GMP level. However, the mechanism for SiaD activation by SiaC remains elusive. Here we determine the crystal structure of SiaC-SiaD-GpCpp complex and revealed a unique mirror symmetric conformation: two SiaD form a dimer with long stalk domains, while four SiaC bind to the conserved motifs on the stalks of SiaD and stabilize the conformation for further enzymatic catalysis. Furthermore, SiaD alone exhibits an inactive pentamer conformation in solution, demonstrating that SiaC activates SiaD through a dynamic mechanism of promoting the formation of active SiaD dimers. Mutagenesis assay confirmed that the stalks of SiaD are necessary for its activation. Together, we reveal a novel mechanism for DGC activation, which clarifies the regulatory networks of c-di-GMP signaling.

中文翻译：

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铜绿假单胞菌结合配偶体激活双鸟苷酸环化酶的结构基础

环二鸟苷单磷酸 (c-di-GMP) 是与铜绿假单胞菌急性-慢性感染转变相关的重要效应物. 以前，我们报道了一个信号网络 SiaABCD，它通过调节 c-di-GMP 水平来调节生物膜的形成。然而，SiaC 激活 SiaD 的机制仍然难以捉摸。在这里，我们确定了 SiaC-SiaD-GpCpp 复合物的晶体结构，并揭示了独特的镜像对称构象：两个 SiaD 形成具有长茎结构域的二聚体，而四个 SiaC 与 SiaD 茎上的保守基序结合并稳定构象以进一步酶催化。此外，单独的 SiaD 在溶液中表现出无活性的五聚体构象，表明 SiaC 通过促进活性 SiaD 二聚体形成的动态机制激活 SiaD。诱变试验证实 SiaD 的茎是其激活所必需的。我们一起揭示了 DGC 激活的新机制，