A high-throughput screening platform for engineering poly(ethylene terephthalate) hydrolases

The ability of enzymes to hydrolyze the ubiquitous polyester, poly(ethylene terephthalate) (PET), has enabled the potential for bio-industrial recycling of this waste plastic. To date, many of these PET hydrolases have been engineered for improved catalytic activity and stability, but current screening methods have limitations in screening large libraries, including under high temperature conditions. Here, we developed a platform that can simultaneously interrogate PET hydrolase libraries of 10⁴-10⁵ variants (per round) for protein solubility, thermostability, and activity via paired, plate-based split green fluorescent protein and model substrate screens. We then applied this platform to improve the performance of a benchmark PET hydrolase, leaf-branch compost cutinase, by directed evolution. Our engineered enzyme exhibited higher catalytic activity relative to the benchmark, LCC-ICCG, on amorphous PET film coupon substrates (~9.4% crystallinity) in pH-controlled bioreactors at both 65 °C (8.5% higher conversion at 48 hours and 38% higher maximum rate, at 2.9% substrate loading) and 68 °C (11.2% higher conversion at 48 hours and 43% higher maximum rate, at 16.5% substrate loading), up to 48 hours, highlighting the potential of this screening platform to accelerate enzyme development for PET recycling.