About This Project

Chemical deconstruction of plastics is a key strategy for fighting waste accumulation and increasing recycling viability. In recent years, enzymes have been discovered that can degrade the plastic polyethylene terephthalate (PET), but the natural enzymes (PETases) unravel at the elevated temperatures required for efficient PET degradation. We aim to design PETases using new generative AI-based methods, to deliver ultrastable, efficient plastic degrading enzmyes.

Ask the Scientists

What is the context of this research?

Chemical deconstruction (1) of plastic is an attractive solution to the plastic accumulation problem (2). Enzymatic deconstruction of the plastic polyethylene terephthalate (PET) has gained significant traction in recent years after the discovery of PET degrading organisms (3, 4). However, optimal enzymatic PET hydrolysis requires high temperatures, which allows penetration of the enzyme into the rigid plastic (5). Natural enzymes are not evolved to operate at these temperatures, limiting their activity. Further, current studies have only focused on several structurally related enzymes (4).

Ultimately, a broader exploration of sequence, structure, and mechanistic space might yield PET degrading enzymes that meet the requirements for process-scale plastic chemical recycling.

What is the significance of this project?

Enzymes that depolymerize PET (PETases) have been discovered, but their thermal stability and catalytic efficiency have limited their applicability (4). Further, different plastic formulations and compositions have differing reactivity profiles between PETases (5). Systematic understanding of the structure function relationships in PET deconstruction will be crucial for engineering efficient PETases.

Computational protein design tools have been applied to PETases (6) with the goal of increasing their thermal stability. Ground-up de novo protein design (7) could instead deliver ultrastable PETases. Emerging AI-generative models of protein design (8) and active site design (9) have revolutionized the field and could enable first-in-class enzymes with entirely new structures and mechanisms.

What are the goals of the project?

While exact benchmarks for PET degradation depend on plastic source and the operating temperature, there are some clear goals based on the state-of-the-art (5, 10, 11).

AI-based protein design will be combined with rational protein engineering and high-throughput evolution in order to arrive at novel, ultrastable, highly active PETases.

High thermal stability:

·T_m > 90 °C (5)

·14-day half-life at 80 °C (5)

Amenable to different post-consumer waste products:

·Operates on bulk material (i.e. water bottle)

·Operates on crystalline and semicrystalline PET

·Selectively deconstruct PET in mixed plastic samples

High activity:

·k_cat/k_M > 2x10⁴ M^-1 s^-1 (10)

Beyond these goals, new structures and mechanisms for PET deconstruction will inform further engineering endeavors.