Polyketide synthases assemble diverse natural products with numerous important applications. The thioester intermediates in polyketide assembly are covalently tethered to acyl carrier protein domains of the synthase. Several mechanisms for polyketide chain release are known, contributing to natural product structural diversification. Here, we report a dual transacylation mechanism for chain release from the enacyloxin polyketide synthase, which assembles an antibiotic with promising activity against Acinetobacter baumannii. A non-elongating ketosynthase domain transfers the polyketide chain from the final acyl carrier protein domain of the synthase to a separate carrier protein, and a non-ribosomal peptide synthetase condensation domain condenses it with (1S,3R,4S)-3,4-dihydroxycyclohexane carboxylic acid. Molecular dissection of this process reveals that non-elongating ketosynthase domain-mediated transacylation circumvents the inability of the condensation domain to recognize the acyl carrier protein domain. Several 3,4-dihydroxycyclohexane carboxylic acid analogues can be employed for chain release, suggesting a promising strategy for producing enacyloxin analogues.
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The genome sequence of B. ambifaria BCC0203 has been deposited in the European Nucleotide Archive (accession no. ERS782625). All other data are available from the authors upon request.
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This research was supported by grants from the BBSRC (BB/L021692/1 to G.L.C., E.M. and J.P. and BB/K002341/1 to G.L.C.), the European Commission (through a Marie Sklodowska-Curie Fellowship to J.M., contract no. 656067) and the Research Foundation Flanders (to J.M.). Support from the University of Warwick through a fellowship from the Institute of Advanced Study (to P.K.S.) and a PhD studentship (to C.H.) is acknowledged. The Bruker maXis Impact and maXis II UHPLC-ESI-Q-TOF-MS systems used in this research were funded by the BBSRC (BB/K002341/1 and BB/M017982/1, respectively). G.L.C. is the recipient of a Wolfson Research Merit Award from the Royal Society (WM130033). Z.L.Y. was funded by a Cardiff University Undergraduate Research Opportunities Programme (CUROP) award to C.J. and E.M. The authors thank M. Tosin for providing the Sfp, PanK, PPAT and DPCK expression vectors. Correspondence and requests for materials should be addressed to G.L.C.
The broad substrate specificity of Bamb_5915, exploited for the production of enacyloxin analogues, is the subject of International (PCT) Patent Application no. PCT/GB2018/051058 (applicant, University of Warwick; inventors, G.L.C., J.M., C.H., X. Jian; status of application, filed 23 April 2018).
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Nature Chemistry (2019)