Molecular basis of binding between the global post-transcriptional regulator CsrA and the T3SS chaperone CesT

Area of Science:

• Molecular Microbiology
• Bacterial Pathogenesis
• Protein-RNA Interactions

Background:

• The Type III Secretion System (T3SS) chaperone CesT interacts with the post-transcriptional regulator CsrA.
• This interaction modulates signaling in enteropathogenic and enterohemorrhagic Escherichia coli, but the molecular basis is unknown.
• CsrA is a key regulator controlling gene expression by binding to mRNA.

Purpose of the Study:

• To elucidate the molecular basis of the CesT/CsrA interaction.
• To determine how CesT binding to CsrA affects CsrA's regulatory function.

Main Methods:

• Construction of a recombinant CsrA-dimer (Re-CsrA) with a single CesT binding site.
• Determination of the atomic structure of the CesT/Re-CsrA complex using X-ray crystallography.
• Analysis of CesT dimerization and its interaction interface with CsrA.

Main Results:

• CesT and CsrA form irregular multimeric complexes in solution through their homodimers.
• CesT adopts a unique dimeric architecture with a C-terminal helix swap for CsrA binding.
• CesT binds to a surface on CsrA that overlaps with the CsrA mRNA binding site.

Conclusions:

• The study reveals the atomic details of CesT-CsrA complex formation.
• CesT modulates CsrA function by competitively inhibiting CsrA's binding to mRNA.
• This provides a molecular mechanism for CesT-mediated regulation of CsrA activity in E. coli pathogenesis.