Cyclic Diguanylate, A Novel Secondary Messenger in Bacteria

微生物基因组学揭示了许多功能未知的保守蛋白质结构域，这表明微生物生理、代谢和行为的重要领域仍未被探索。这项研究旨在研究含有GGDEF和EAL结构域的蛋白质的功能，这两个结构域在不同的细菌中广泛分布。GGDEF和EAL结构域参与了不寻常的核苷酸c-di-GMP的合成和水解。这个项目的主要假设是，c-di-GMP是细菌中一种重要的、被低估的第二信使。该项目的长期目标是阐明c-di-GMP的作用，并以代谢多功能的球状红杆菌为模型揭示其运作机制。初步数据表明，球藻含有参与c-di-GMP合成和水解酶的酶(双鸟苷环化酶)和水解酶(磷酸二酯酶)。本项目最初的重点将放在球藻c-di-GMP特异性的两种磷酸二酯酶上，命名为BphG和BphH，它们含有光敏色素类型域，可能代表独特结构的光感受器。球形乳杆菌细胞内c-di-GMP池的耗尽导致球形乳杆菌转录组的特异性改变。揭示c-di-GMP影响基因表达的机制是该项目的另一个目标。这项研究将结合分子遗传学、转录学和生化方法来解决这些问题。这项研究将填补我们对细菌细胞理解的一个明显空白，这是由于忽视了潜在的重要第二信使c-di-GMP。阐明c-di-GMP的作用有望在各种细菌的信号转导领域产生重大影响，包括在农业、环境和医学上具有重要意义的物种。该项目将为高中、本科生、研究生和博士后的跨学科培训提供充足的机会。

The numerous conserved protein domains of unknown function have been revealed through microbial genomics, which suggests that significant areas of microbial physiology, metabolism and behavior remain unexplored. This research is aimed at investigating functions of proteins containing GGDEF and EAL domains that are broadly distributed in diverse bacteria. The GGDEF and EAL domains are involved in synthesis and hydrolysis of the unusual nucleotide, cyclic diguanylate, c-di-GMP. The main hypothesis of this project is that c-di-GMP is an important underappreciated second messenger in bacteria. The long-term goals of the project are to elucidate the role of c-di-GMP and to reveal the mechanisms by which it operates using the metabolically versatile proteobacterium, Rhodobacter sphaeroides, as a model. Preliminary data indicate that R. sphaeroides contains enzymes involved in both synthesis (diguanylate cyclases) and hydrolysis (phosphodiesterases) of c-di-GMP. Initial emphasis of this project will be placed on two R. sphaeroides c-di-GMP-specific phosphodiesterases, designated BphG and BphH, which contain phytochrome-type domains and are likely to represent photoreceptors of unique structure. The depletion of the intracellular pool of c-di-GMP in R. sphaeroides results in specific changes in the R. sphaeroides transcriptome. Uncovering mechanisms by which c-di-GMP affects gene expression is another aim of this project. A combination of molecular genetic, transcriptomics and biochemical approaches will be employed to address these questions.This research will fill an apparent void in our understanding of the bacterial cell resulting from an oversight of a potentially important second messenger, c-di-GMP. Elucidation of the role of c-di-GMP is anticipated to have a significant effect on the field of signal transduction in various bacteria, including agriculturally, environmentally and medically important species. This project will provide ample opportunities for interdisciplinary training of high school, undergraduate, graduate and postdoctoral students.