Analysis of structure-function relationships in the colibactin-maturating enzyme ClbP

pks genomic island of Escherichia coli is involved in the synthesis of the non-ribosomal peptide-type genotoxin colibactin, which has been suggesting as affecting the host immune response and having an impact on cancer development. The pks-encoded enzyme ClbP is an atypical peptidase that contributes to the synthesis of colibactin. In this work, we identified key features of ClbP. Bacterial fractionation and Western-blot analysis revealed the docking of ClbP to the bacterial inner membrane via a C-terminal domain harboring three predicted transmembrane helices. Whereas only one helix was necessary for the location in the inner membrane, the complete sequence of the C-terminal domain was necessary for ClbP bioactivity. In addition, the N-terminal sequence of ClbP allowed the SRP/Sec/YidC- and MreB-dependent translocation of the enzymatic domain in the periplasmic compartment, a feature also essential for ClbP bioactivity. Finally, the comparison of ClbP structure with that of the paralogs FmtA-like and AmpC revealed at an extremity of the catalytic groove a negative electrostatic potential surface characteristic of ClbP. Site-directed mutagenesis experiments identified in this zone two aspartic residues that were important for ClbP bioactivity. Overall, these results suggest a model for precolibactin activation by ClbP and pave a way for the design of inhibitors targeting colibactin production.