Colibactin is an uncharacterized secondary metabolite produced by certain strains of E. coli present in the human gut. It induces double-stranded DNA breaks in eukaryotic cells and promotes colorectal cancer and tumor formation under host inflammatory conditions. The colibactin biosynthetic pathway has been studied extensively by various groups since its discovery nearly a decade ago. The 54 kb gene cluster (pks island) encodes a non-ribosomal peptide synthetase-polyketide synthase (NRPS-PKS) assembly line and includes three NRPSs (ClbH, J, N), three PKSs (ClbC, I, O), two NRPS/PKS hybrids (ClbB, K), accessory proteins (ClbA, D, E, F, G, L, P, Q, R, S) and a transporter ClbM. The biosynthesis involves a prodrug-like resistance strategy where the inactive genotoxin is transported to the periplasm, cleaved and processed to the active form.
We have successfully characterized (structurally and functionally) ClbM, ClbQ and ClbS. Currently, we are working to identify the roles of the remaining uncharacterized genes in the pathway utilizing structural biology.