A Mechanistic Model for Colibactin-Induced Genotoxicity

Area of Science:

• Microbiology
• Natural Product Chemistry
• Molecular Biology

Background:

• Colibactins are natural products from E. coli linked to DNA damage.
• The clb gene cluster, responsible for colibactin production, is present in both pathogenic and probiotic E. coli strains.
• Precolibactins are proposed precursors to genotoxic colibactins, but their structure and activity remain unconfirmed.

Purpose of the Study:

• To synthesize and evaluate colibactin derivatives to determine their DNA alkylation activity.
• To test the hypothesis that colibactins are unsaturated imines that alkylate DNA via cyclopropane ring opening.
• To elucidate the structural requirements for colibactin-mediated DNA damage.

Main Methods:

• Synthesis of 13 synthetic colibactin derivatives.
• In vitro evaluation of DNA binding and alkylation activity of synthesized compounds.
• Comparative analysis of imine and pyridone derivatives.

Main Results:

• Unsaturated imine derivatives, but not pyridone-containing precolibactins, potently alkylate DNA.
• The imine, unsaturated lactam, and cyclopropane functionalities are essential for DNA alkylation.
• A cationic residue was found to enhance DNA alkylation activity.
• Pyridone derivatives appear to be off-pathway products formed in the absence of functional colibactin peptidase (ClbP).

Conclusions:

• The genotoxicity associated with the clb gene cluster is mediated by unsaturated imine colibactins, not pyridone-containing precolibactins.
• Structural features like the imine, unsaturated lactam, and cyclopropane are critical for DNA alkylation.
• Understanding the precise structures responsible for DNA damage is key to connecting clb+ E. coli phenotypes to specific metabolites.