Biosensor Guided Polyketide Synthase Engineering for Optimization of Domain Exchange Boundaries

Abstract Type I modular polyketide synthases (PKSs) are multi-domain enzymes functioning like assembly lines. Many engineering attempts have been made for the last three decades to replace, delete and insert new functional domains into PKSs to produce novel molecules. However, the resulting PKS hybrids typically have reduced catalytic activities and are often insoluble due to misfolding. Here, we have developed a fluorescence-based biosensor method for detecting engineered PKSs with high solubility. The biosensor has been used to sort through PKS hybrids that had acyltransferase (AT) domains from other PKSs exchanged for the native AT with randomly assigned linker junctions. Importantly, we observed a significant correlation between activity and solubility. Evaluation of highly soluble mutants in vitro revealed new boundaries for AT domain exchanges that give a wild-type level of catalytic activity. Together, we have successfully developed an experimentally validated high-throughput method to efficiently screen active engineered PKSs that produce target molecules.