The DctA/DcuS sensor complex of Escherichia coli: The components and their function

细菌能够使用大量的膜结合的传感蛋白来检测环境刺激。大肠杆菌的敏感蛋白激酶DCU(C4-二羧酸摄取传感器)具有典型的膜结合的敏感蛋白、周质敏感蛋白和胞质蛋白激酶域的组成。感觉域是与效应器富马酸或其他C4-二羧酸盐结合的PAS结构域。然而，DCUS还需要二次通透性作为功能的共同传感器。琥珀酸转运体DCTA和富马酸/琥珀酸逆向转运体DCuB在好氧和厌氧条件下发挥这一功能，分别形成传感器复合体DCTA/DCU或DCuB/DCU。DCTA(或DCuB)与DCU之间的相互作用取决于已确定的渗透层的特定结构域。这项工作表明，DCTA/DCU和DCuB/DCUS传感器复合体一方面通过与富马酸结合在质膜周围的PAS结构域上直接响应刺激分子(富马酸)的存在，而DCTA或DCuB介导有关运输状态的信息，从而调节DCU的代谢状态。这种新型的转运蛋白/传感器复合体的功能需要在体内和体外进行研究，以便在分子水平上了解传感器复合体的功能。在渗透酶方面，未来的研究将集中在DCTA上，因为这种转运蛋白比厌氧转运蛋白DcuB更容易操作和研究。DCTA/DCUS传感器复合体的传感器和转运蛋白可以被纯化并在脂质体中重组。DCUS和DCTA应在体内、体外单独和在复合体中进行研究。一个主要主题将是传感器DCU和传送器DCTA在传感中的不同角色的问题，为什么除了传感器之外还需要传送器来进行信号感知，以及传送器的功能状态如何传输到传感器DCU。有突变体可以改变DCU的效应器特异性，这将表明DCU是否单独负责C4-二羧酸盐的传感。DCTA的helix8/helix8b区域似乎与转运蛋白(Helix8)的运输部位相连，helix8b与传感器DCU相互作用。我们将详细研究该区域在向传感器传递DCTA运输状态和功能状态信息方面的作用。我们希望DCTA/DCUS传感器复合体的工作将能够提供对这些新型转运体/传感器复合体的详细了解。似乎利用分子和代谢状态的双重刺激来控制这类传感器的功能状态，这可能是细菌和其他生物体中传感器信号感知和控制的一种重要和更一般的模式。

Bacteria are able to use a large number of membrane-bound sensor kinases for detecting environmental stimuli. The sensor kinase DcuS (C4-dicarboxylate uptake sensor) of Escherichia coli has the typical composition of a membrane bound sensor kinase with a periplasmic sensing and a cytoplasmic kinase domain. The sening domain is a PAS domain which binds the effector fumarate or other C4-dicarboxylates. DcuS requires, however, in addition secondary permeases as co-sensors for function. The succinate transporter DctA and the fumarate/succinate antiporter DcuB serve this function under aerobic and anaerobic conditions, and form sensor complexes DctA/DcuS or DcuB/DcuS, respectively. The interaction between DctA (or DcuB) and DcuS depends on specific domains of the permeases that have been identified. The work suggests that the DctA/DcuS and DcuB/DcuS sensor complexes responds to the presence of the stimulus molecule (fumarate) on the one hand directly by binding the fumarate at the periplasmic PAS domain, whereas DctA or DcuB mediate information on the transport status, and thus on the metabolic state, to DcuS. The function of this novel type of transporter/sensor complex shall be studied in vivo and in vitro in order to understand the function of the sensor complex on a molecular level. On the permease side, future studies will concentrate on DctA since this transporter can be handled and studied much easier than the anaerobic transporter DcuB.The sensor and transporter proteins of the DctA/DcuS sensor complex can be purified and reconstituted in liposomes. DcuS and DctA shall be studied in vivo and in vitro singly and in the complex. A major topic will be the question for the different roles of the sensor DcuS and of the transporter DctA in sensing, why the transporter is required in addition to the sensor for signal perception, and how the functional state of the transporter is transmitted to the sensor DcuS. Mutants are available that change the effector specificity of DcuS which will show whether DcuS alone is responsible for C4-dicarboxylate sensing. The helix8/helix8b region of DctA appears to be linked to the transport site of the transporter (helix8), and helix8b interacts with the sensor DcuS. The role of this region in transmitting the information on the transport status and functional state of DctA to the sensor will be studied in detail.We hope that work on the DctA/DcuS sensor complex will be able to provide a detailed understanding of these novel transporter/sensor complexes. It appears that dual stimuli (molecules and metabolic state) are used to control the functional state of this type of sensors, and this might be an important and more general mode of signal perception and control of sensors in bacteria and other organisms.