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Citrate Sensing by the C₄-Dicarboxylate/Citrate Sensor Kinase DcuS of Escherichia coli: Binding Site and Conversion of DcuS to a C₄-Dicarboxylate- or Citrate-Specific Sensor

Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany,¹ Max Planck-Institut für Biophysikalische Chemie, 37077 Göttingen, Germany,² Max Planck-Institut für Entwicklungsbiologie, 72076 Tübingen, Germany³

Received 1 February 2007/ Accepted 19 March 2007

The histidine protein kinase DcuS of Escherichia coli senses C₄-dicarboxylates and citrate by a periplasmic domain. The closely related sensor kinase CitA binds citrate, but no C₄-dicarboxylates, by a homologous periplasmic domain. CitA is known to bind the three carboxylate and the hydroxyl groups of citrate by sites C1, C2, C3, and H. DcuS requires the same sites for C₄-dicarboxylate sensing, but only C2 and C3 are highly conserved. It is shown here that sensing of citrate by DcuS required the same sites. Binding of citrate to DcuS, therefore, was similar to binding of C₄-dicarboxylates but different from that of citrate binding in CitA. DcuS could be converted to a C₄-dicarboxylate-specific sensor (DcuS_DC) by mutating residues of sites C1 and C3 or of some DcuS-subtype specific residues. Mutations around site C1 aimed at increasing the size and accessibility of the site converted DcuS to a citrate-specific sensor (DcuS_Cit). DcuS_DC and DcuS_Cit had complementary effector specificities and responded either to C₄-dicarboxylates or to citrate and mesaconate. The results imply that DcuS binds citrate (similar to the C₄-dicarboxylates) via the C₄-dicarboxylate part of the molecule. Sites C2 and C3 are essential for binding of two carboxylic groups of citrate or of C₄-dicarboxylates; sites C1 and H are required for other essential purposes.

Published ahead of print on 6 April 2007.