Mutated enzyme breaks down plastic more efficiently

Poly(ethylene terephthalate), or PET, is widely used in beverage bottles, clothing, packaging, and carpeting. After use, much of the plastic finds its way into landfills or becomes pollution, such as in the Great Pacific garbage patch. Used PET can be broken down chemically and reused, but the process is not widely employed because buying new PET is cheaper. Two years ago, a Japanese group found a bacterium that uses two enzymes to degrade and assimilate PET: PETase converts PET to mono(2-hydroxyethyl) terephthalic acid (MHET), and MHETase breaks down MHET into terephthalic acid and ethylene glycol. H. Lee Woodcock of the University of South Florida, John E. McGeehan of the University of Portsmouth, Gregg T. Beckham of the National Renewable Energy Laboratory, and coworkers obtained high-resolution X-ray crystal structures of PETase. They also discovered that it degrades the emerging PET replacement polyethylene-2,5-furandicarboxylate (PEF), and they mutated the enzyme into a more efficient version (Proc. Natl. Acad. Sci. USA 2018, DOI: 10.1073/pnas.1718804115). The native enzyme’s PET-degrading activity is too low for industrial use, but the mutant degrades PET about 20% more efficiently—suggesting that further optimization could lead to a commercial bioremediation system. After further enzyme engineering, the group plans to scale up this process to the pilot scale at NREL and work with industrial partners to take it beyond that point, Beckham says.