环二鸟苷酸(c-di-GMP)和环磷酸腺苷(cAMP)都是生物体内重要的第二信使，在原核生物中，环二鸟苷酸对细菌游动性、病原微生物感染、生物被膜形成和细胞周期均具有极其重要的调控作用，其合成和降解分别受鸟苷酸环化酶(DGC)和磷酸二酯酶(PDE)的控制，这些酶具有庞大的结构域组成和功能多样性。第二信使cAMP与camp受体蛋白(crp)共同构成了一种细菌全局调节因子，参与了分解代谢的抑制和许多未知基因的表达调控。其合成主要由腺苷酸环化酶(adenylate cyclase，CyaA)催化。cAMP在细胞内的水平还受cAMP磷酸二脂酶和排出机制影响，然而这两种信号之间是否存在互相调控或者交叉调控的现象并不清楚。
本研究首先发现了一个新的通过调控局部c-di-GMP水平来影响细菌游动性的鸟苷酸环化酶GcsA，该基因转录同时受到c-di-GMP和cAMP水平的调控。通过分子遗传学手段、凝胶阻滞和DNA足迹实验，证实GcsA受c-di-GMP/FleQ途径的间接调控而受cAMP/CRP途径的直接调控。有趣的是c-di-GMP水平能够影响细胞中cAMP水平的变化，但c-di-GMP对GcsA的调控并不依赖于cAMP水平的变化，这暗示c-di-GMP和cAMP对GcsA的调控途径是非冗余的，也为进一步研究c-di-GMP和cAMP信号之间的相互关系及其对原核生物生命过程调控的分子机制拉开了序幕，相关论文最近被环境微生物学知名期刊《Environmental Microbiology》接收，论文第一作者为博士后肖玉杰。
论文链接：https://onlinelibrary.wiley.com/doi/abs/10.1111/1462-2920.14832
（文/罗雪松）
Summary
The ubiquitous bacterial second messenger c‐di‐GMP is synthesized by diguanylate cyclase (DGC) and degraded by phosphodiesterase (PDE). Pseudomonas putida has dozens of DGC/PDE‐encoding genes in its genome, but the phenotypical‐genotypical correlation and transcriptional regulation of these genes are largely unknown. Herein, we characterize function and transcriptional regulation of a P. putida c‐di‐GMP‐metabolizing enzyme, GcsA. GcsA consists of two PAS domains, followed by a canonical GGDEF domain and a truncated EAL domain. In vitro analysis confirmed the DGC activity of GcsA. The phenotypic observation revealed that GcsA inhibited swimming motility in a FlgZ‐dependent manner. In terms of transcriptional regulation, gcsA was found to be cooperatively regulated by c‐di‐GMP and cAMP via their effectors, FleQ and Crp, respectively. The transcription of gcsA was promoted by c‐di‐GMP and inhibited by cAMP. In vitro binding analysis revealed that FleQ indirectly regulated the transcription of gcsA, while Crp directly regulated the transcription of gcsA by binding to its promoter. Besides, an inverse relationship between the cellular c‐di‐GMP and cAMP levels in P. putida was confirmed. These findings provide basic knowledge regarding the function and transcriptional regulation of GcsA and demonstrate a crosstalk between c‐di‐GMP and cAMP in the regulation of the expression of GcsA in P. putida.