Computationally-Aided and Polyketide Synthase-Based Controlled Synthesis of Polycyclopropanated Fuel Molecules

Reducing carbon emissions from aviation and long-distance transportation sectors requires the development of sustainable biofuels with suitable energy density, freezing point, and other physical properties. We previously demonstrated biological production of high energy polycyclopropanated fatty acids (POP-FAs, class I) using an iterative polyketide synthase (iPKS) pathway in a Streptomyces host. Here, we used a computational model of fuel properties to design POP-FA products that are better for biofuel applications than the previously produced POP-FAs. Then, we modified the chain length and cyclopropane ratio of POP-FAs by in vivo gene exchange, highlighting cyclopropanase (CP) catalysis to be key for POP-FA engineering. Leveraging both natural and engineered pathway product diversity, we demonstrate targeted production of new classes of POP-FAs, namely shortened POP-FAs (class II) with distinct cyclopropane positions, as well as fully cyclopropane-saturated POP-FAs (class III). Compared to class I POP-FAs, shortened class II POP-FAs are predicted to have superior freezing point properties for aviation, while class III POP-FAs should have superior energy-density. These precise and controllable modifications to POP-FA structure open the door for bioproduction of designer POP fuels.