MOLECULAR MECHANISM OF OSMOTIC REGULATION IN PROKARYOTIC AND EUKARYOTIC MICROORGANISMS

总的来说，蛋白质磷酸化是最广泛使用的调节生物过程的机制之一，包括细胞内的信号转导。在真核生物中，涉及许多蛋白质酪氨酸或丝氨酸/苏氨酸激酶的蛋白质磷酸化和去磷酸化事件的级联已经得到了很好的研究。相比之下，最近的密集研究表明，细菌设计了一种完全不同的磷转移信号机制，以引发对环境的各种适应性反应。这种细菌信号转导机制最初被称为“双组分调控系统”。“敏感蛋白激酶”与其同源的磷酸受体“反应调节蛋白”之间的分子通讯方式主要是基于组氨酸到天冬氨酸(His-Asp)的磷酸转移。例如，在大肠杆菌中，至少有30个不同的感受器-调节器对在各种不同的适应性反应中工作。这种特殊的信号转导机制曾被认为仅限于原核生物。然而，最近在不同的真核物种中发现了许多例子。此外，最近的研究表明，细菌信号转导的分子机制并不像以前认为的那样简单，实际上比以前认为的要复杂得多。这一新概念应称为“多步组氨酸-天冬氨酸磷酸转移信号机制”。在这个特别的项目中，我们广泛地分析了原核和真核微生物的这种信号转导机制，特别是它们的渗透调节。

In general, protein phosphorylation is one of the most widely used mechanisms for regulating biological processes, including intracellular signal transduction. In eukaryotes, the cascades of protein phosphorylation and dephosphorylation events involving a number of protein tyrosine or serine/threonine kinases have been well studied. In contrast, recent intensive studies revealed that bacteria have devised a quite different phosphotransfer signaling mechanism for eliciting a variety of adaptive responses to their environment. Such a bacterial signal transduction mechanism was originally referred to as a "two-component regulatory system". The mode of molecular communication between a "sensor kinase" and its cognate phospho-accepting "response regulator" is principally based on histidine-to-aspartate (His-Asp) phosphotransfer. In Escherichia coli, for example, at least thirty different sensor-regulator pairs operate in a wide variety of adaptive responses. This particular signal transduction mechanism was once thought to be restricted to prokaryotes. However, many instances have recently been uncovered in diverse eukaryotic species. Furthermore, recent studies suggested that the molecular mechanism underlying the bacterial signal transduction is not simple as, and, in fact, is more sophisticated than thought previously. The new concept should be referred to as the "multi-step His-Asp phosphotransfer signaling mechanism". In this particular project, we extensively analyzed such signal transduction mechanisms both for prokaryotic and eukaryotic microorganisms, with special reference to their osmotic regulation.