Rational Domain Swaps Reveal Insights about Chain Length Control by Ketosynthase Domains in Fungal Nonreducing Polyketide

ABSTRACT: A facile genetic methodology in the filamentous fungus Aspergillus nidulans allowed exchange of the starter unit ACP transacylase (SAT) domain in the nonreduced polyketide synthase (NR-PKS) AfoE of the asperfuranone pathway with the SAT domains from 10 other NR-PKSs. The newly created hybrid with the NR-PKS AN3386 is able to accept a longer starter unit in place of the native substrate to create a novel aromatic polyketide in vivo. Fungal polyketides are generated by multidomain iterativetype I polyketide synthases (PKSs), in which catalytic domains are covalently linked. At a minimum, ketosynthase (KS), acyl transferase (AT), and acyl carrier protein domains (ACP) are featured. Fungal PKSs may be nonreduced, partially reduced, or highly reduced, based on the overall domain composition. Nonreduced PKSs (NR-PKSs) additionally contain starter unit ACP transacylase (SAT) and product template (PT) domains and may also contain a methyltransfer