Institute for Microbiology and Infection, School of Biosciences, University of Birmingham, Birmingham, B15 2TT, UK.
Nat Commun. 2019 Sep 9;10(1):4086. doi: 10.1038/s41467-019-12051-6.
The bacterial second messenger cyclic-di-GMP is a widespread, prominent effector of lifestyle change. An example of this occurs in the predatory bacterium Bdellovibrio bacteriovorus, which cycles between free-living and intraperiplasmic phases after entering (and killing) another bacterium. The initiation of prey invasion is governed by DgcB (GGDEF enzyme) that produces cyclic-di-GMP in response to an unknown stimulus. Here, we report the structure of DgcB, and demonstrate that the GGDEF and sensory forkhead-associated (FHA) domains form an asymmetric dimer. Our structures indicate that the FHA domain is a consensus phosphopeptide sensor, and that the ligand for activation is surprisingly derived from the N-terminal region of DgcB itself. We confirm this hypothesis by determining the structure of a FHA:phosphopeptide complex, from which we design a constitutively-active mutant (confirmed via enzyme assays). Our results provide an understanding of the stimulus driving DgcB-mediated prey invasion and detail a unique mechanism of GGDEF enzyme regulation.
细菌第二信使环二鸟苷酸（cyclic-di-GMP）是生活方式改变的广泛而显著的效应因子。捕食性细菌蛭弧菌（Bdellovibrio bacteriovorus）就是一个例子，它在进入（并杀死）另一种细菌后，会在自由生活和周质内阶段之间循环。猎物入侵的开始由 DgcB（GGDEF 酶）控制，该酶会对未知刺激产生环二鸟苷酸。在这里，我们报告了 DgcB 的结构，并证明 GGDEF 和感应 forkhead 相关（FHA）结构域形成不对称二聚体。我们的结构表明，FHA 结构域是一个公认的磷酸肽传感器，而激活配体出人意料地来自 DgcB 自身的 N 端区域。我们通过确定 FHA:磷酸肽复合物的结构证实了这一假设，并从该结构设计了一个组成型激活突变体（通过酶测定法确认）。我们的结果提供了对驱动 DgcB 介导的猎物入侵的刺激的理解，并详细描述了 GGDEF 酶调节的独特机制。
