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

• Applicant: Professor Dr. Gottfried Unden
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2008 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 59122837

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.

• DFG Programme: Research Grants