P127: Novel enzymes in the anticancer antibiotic leinamycin biosynthetic pathway

Leinamycin (LNM) exhibits potent anti-tumor activity in murine tumor models.  More importantly, tumors resistant to clinical anticancer drugs such as cisplatin, doxorubicin, mitomycin, and cyclophosphamide are susceptible to LNM.  The powerful anticancer action of LNM is attributed to a dithiolane moiety that undergoes rearrangement to produce an unstable episulfonium ion intermediate capable of DNA alkylation.  This dithiolane moiety is appended to a lactam ring backbone, which is generated by the action of a hybrid non-ribosomal peptide synthetase/polyketide synthase (NRPS/PKS).  There are three main events in dithiolane moiety generation: (I) installation of a β-propionyl group, (II) sulfur addition into the backbone, (III) tailoring steps to finalize the ring.  With respect to (I), we have determined LnmK to be a novel bifunctional acyltransferase/decarboxylase (AT/DC) responsible for production of propionyl-S-ACP from methylmalonyl-CoA to initiate β-branching.  With respect to (II), we have determined that LnmJ-SH, a domain embedded in the PKS, is capable of sulfide generation utilizing cysteine.  We are currently using structural biology to understand the novel chemistry performed by these enzymes, determine their combinatorial biosynthetic potential and possibly generate derivatives of LNM using structure guided activity reprogramming.