The cytoplasmic PAS _C domain of the sensor kinase DcuS of Escherichia coli: role in signal transduction, dimer formation, and DctA interaction

Abstract

The cytoplasmic PAS _C domain of the fumarate responsive sensor kinase DcuS of Escherichia coli links the transmembrane to the kinase domain. PAS _C is also required for interaction with the transporter DctA serving as a cosensor of DcuS. Earlier studies suggested that PAS _C functions as a hinge and transmits the signal to the kinase. Reorganizing the PAS _C dimer interaction and, independently, removal of DctA, converts DcuS to the constitutive ON state (active without fumarate stimulation). ON mutants were categorized with respect to these two biophysical interactions and the functional state of DcuS: type I-ON mutations grossly reorganize the homodimer, and decrease interaction with DctA. Type IIA-ON mutations create the ON state without grossly reorganizing the homodimer, whereas interaction with DctA is decreased. The type IIB-ON mutations were neither in PAS _C/PAS _{C ,} nor in DctA/DcuS interaction affected, similar to fumarate activated wild-typic DcuS. OFF mutations never affected dimer stability. The ON mutations provide novel mechanistic insight: PAS _C dimerization is essential to silence the kinase. Reorganizing the homodimer and its interaction with DctA activate the kinase. The study suggests a novel ON homo-dimer conformation (type IIB) and an OFF conformation for PAS _C. Type IIB-ON corresponds to the fumarate induced wild-type conformation, representing an interesting target for structural biology.