Structure of the two‐component response regulator RcsB‐DNA complex

Abstract

The Rcs phosphorelay is a complex two‐component system in enteric pathogens that achieves transmission of molecular signals through a phosphorylation cascade between two hybrid sensor kinases RcsC‐RcsD and the response regulator RcsB. The latter can form either homodimers or heterodimers with other transcriptional factors. These heterodimers can be phosphorylation‐dependent or –independent. This complexity allows RcsB to regulate the transcription of a diverse array of genes essential for pathogen survival and host invasion. Despite increasing appreciation of the importance of RcsB in pathogenicity, the molecular mechanisms by which RcsB forms homo/heterodimers to facilitate DNA binding in response to different environmental stresses are not well understood. Here, we present the first X‐ray crystal structure of the response regulator RcsB from Escherichia coli in complex with DNA determined at a resolution of 3.4 Å. The structure reveals that non‐phosphorylated RcsB forms an unusual asymmetric dimer in the DNA‐bound state. This asymmetry likely provides conformational flexibility that allows RcsB to interact with a large number of genes and to form heterodimers with other transcriptional regulators. Combining our structural data with electrophoretic mobility shift assays, surface plasmon resonance, and size exclusion chromatography with multi‐angle light scattering analysis provides important details about the molecular mechanism by which the universal two‐component response regulator RcsB recognizes DNA.Support or Funding InformationCSGID is funded by the National Institute of Allergy and Infectious Diseases of NIH under Contracts No. HHSN272200700058C and HHSN272201200026C