Centre for Enzyme Innovation

Biochemical and structural characterization of an aromatic ring-hydroxylating dioxygenase for terephthalic acid catabolism

Kincannon, W. M., Zahn, M., Clare, R., Romberg, A., Larson, J., Lusty-Beech, J., Bothner, B., Beckham, G. T., McGeehan, J. E. & DuBois, J. L. (2022), Proc Natl Acad Sci USA 119, 13, 9 p., e2121426119.

Bioconversion strategies aimed at plastics have emerged as important components of enabling a circular economy for synthetic plastics, especially those that exhibit chemically similar linkages to those found in nature, such as polyesters. The enzyme system described in this work is essential for the efficient uptake of the enzymatic breakdown components of poly(ethylene terephthalate) into bacteria. Our description of its structure and substrate preferences lays the groundwork for in vivo or ex vivo engineering of this system for PET upcycling.

Comparative performance of PETase as a function of reaction conditions, substrate properties, and product accumulation

Erickson, E., Shakespeare, T. J., Bratti, F., Buss, B., Graham, R., Hawkins, M., Koenig, G., Michener, W. E., Miscall, J., Ramirez, K., Rorrer, N. A., Zahn, M., Pickford, A., McGeehan, J. E. & Beckham, G. T. 2022, ChemSusChem 15, 1, 11 p., e202101932.

The past decade has seen incredible progress in the identification, characterization, and engineering of PET hydrolases, including the PETase from Ideonella sakaiensis featured in this study. Now, strategies for implementation and scale-up of enzymatic recycling technologies are on the horizon. As this study points out, in addition to enzyme engineering, reaction optimization and process design tuned to the characteristics of the waste stream may prove critical in realizing an efficient enzymatic recycling process.

Chemical and biological catalysis for plastics deconstruction, recycling, and upcycling

Ellis, L.D., Rorrer, N.A., Sullivan, K.P., Otto, M., McGeehan, J.E., Román-Leshkov, Y., Wierckx, N., Beckham, G.T. 2021, Nature Catalysis 4, 539–556.

In this review we focus on the challenges and opportunities in chemical and biological catalysis for plastics deconstruction, recycling, and upcycling. We stress the need for rigorous characterization and use of widely available substrates, such that catalyst performance can be compared across studies. We draw parallels between catalysis on biomass and plastics, as both substrates are low-value, solid, recalcitrant polymers. Innovations in catalyst design and reaction engineering are needed to overcome kinetic and thermodynamic limitations of plastics deconstruction. Either chemical and biological catalysts will need to act interfacially, where catalysts function at a solid surface, or polymers will need to be solubilized or processed to smaller intermediates to facilitate improved catalyst–substrate interaction. Overall, developing catalyst-driven technologies for plastics deconstruction and upcycling is critical to incentivize improved plastics reclamation and reduce the severe global burden of plastic waste.

Techno-economic, life cycle, and socio-economic impact analysis of enzymatic recycling of poly(ethylene terephthalate)

Singh, A., Rorrer, N.A., Nicholson, S.R., Erickson, E., DesVeaux, J., Avelino, A.F.T., Lamers, P., Bhatt, A., Zhang, Y., Avery, G., Wu, C., Tao, L., Pickford, A.R., Carpenter, A.C., McGeehan, J.E. Beckham, G.T., 2021, Joule 5, 1–25.

Scientists in the UK and US, as part of the BOTTLE Consortium, modelled a conceptual recycling facility where waste PET (polyethylene terephthalate) plastic is broken down with enzymes, returning the material back into its original chemical building blocks. This process was compared with traditional fossil fuel routes, where plastic building blocks are currently extracted mainly from oil and gas. The study reveals that PET produced using enzyme-based recycling can be cost competitive with traditional fossil fuel-derived PET, cut energy use by up to 80 per cent, and reduce climate impacting greenhouse gas emissions by up to 40 per cent relative to virgin manufacturing.

A comprehensive techno-economic analysis and life cycle assessment revealed strong economic, social, and environmental benefits of using enzymes which opens up exciting opportunities for industry to make a step-change in how these plastics are recycled.

Critical enzymatic reactions in aromatic catabolism for microbial lignin conversion

Erickson, E., Bleem, A., Kuatsjah, E., Werner, A.Z., DuBois, J.L., Eltis, L.D., McGeehan, J.E. and Beckham, G.T., 2021, Nature Catalysis 5, 86–98.

There are many parallels between the fields of natural and synthetic plastic polymer break down strategies. Here we look at the key enzymes that can tackle the deconstruction of the common biopolymer lignin, detailing the specific reactions that are necessary for the biological funnelling of aromatic compounds. We review the known enzymatic mechanisms for these reactions that are relevant for aerobic aromatic catabolism of lignin-related monomers, highlighting opportunities at the intersection of biochemistry, enzyme engineering and metabolic engineering for applications in the expanding field of microbial lignin valorisation.

Characterization and engineering of a two-enzyme system for plastics depolymerization

Knott, B.C., Erickson, E., Allen, M.D., Gado, J.E., Graham, R., Kearns, F.L., Pardo, I., Topuzlu, E., Anderson, J.J., Austin, H.P., Dominick, G., Johnson, C.W., Rorrer, N.A., Szostkiewicz, C.J., Copié, V., Payne, C.M., Woodcock, H.L., Donohoe, B.S., Beckham, G.T. & McGeehan, J.E., 2020, Characterization and engineering of a two-enzyme system for plastics depolymerization. Proc Natl Acad Sci USA, 117 (41), 25476–25485.

Deconstruction of recalcitrant polymers, such as cellulose or chitin, is accomplished in nature by synergistic enzyme cocktails that evolved over millions of years. In these systems, soluble dimeric or oligomeric intermediates are typically released via interfacial biocatalysis, and additional enzymes often process the soluble intermediates into monomers for microbial uptake. The discovery of a two-enzyme system for polyethylene terephthalate (PET) deconstruction, which employs one enzyme to convert the polymer into soluble intermediates and another enzyme to produce the constituent PET monomers (MHETase), suggests that nature may be evolving similar deconstruction strategies for synthetic plastics. This study on the characterization of the MHETase enzyme and synergy of the two-enzyme PET depolymerization system may inform enzyme cocktail-based strategies for plastics upcycling.