MOLECULAR MECHANISM OF OSMOTIC REGULATION IN PROKARYOTIC AND EUKARYOTIC MICROORGANISMS

一般而言，蛋白质磷酸化是用于调节生物过程（包括细胞内信号转导）的最广泛使用的机制之一。在真核生物中，涉及许多蛋白酪氨酸或丝氨酸/苏氨酸激酶的蛋白磷酸化和去磷酸化事件的级联反应已经被很好地研究。相比之下，最近的深入研究表明，细菌已经设计了一种完全不同的磷酸转移信号传导机制，用于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“双组分调节系统”。“传感激酶”和其同源磷酸接受“反应调节剂”之间的分子通讯模式主要基于组氨酸至天冬氨酸（His-Asp）磷酸转移。例如，在大肠杆菌中，至少有30种不同的传感器-调节器对在各种适应性反应中发挥作用。这种特殊的信号转导机制一度被认为仅限于原核生物。然而，最近在不同的真核生物物种中发现了许多实例。此外，最近的研究表明，细菌信号转导的分子机制并不简单，事实上，比以前认为的更复杂。这一新概念应称为“多步His-Asp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.