Improving a plastic-degrading enzyme for better recycling

Stabilizing a bacterial enzyme by strategically decorating it with sugars could help it recycle polyethylene terephthalate (PET), the polymer widely used to make plastic water and shampoo bottles (Biochemistry 2018, DOI: 10.1021/acs.biochem.7b01189). The enzyme, called cutinase, breaks down PET into ethylene glycol and terephthalic acid, which can be recovered to make new bottles. But at the optimal PET processing temperature of 75 °C, cutinase begins to unfold and form clumps. To prevent formation of these inactive clumps, Richard A. Gross of Rensselaer Polytechnic Institute and colleagues genetically engineered yeast to produce a cutinase originally isolated from microbes found in leaf and branch compost. The yeast cells naturally glycosylated the enzyme at three sites, adding short strings of sugars. The glycosylated cutinase formed fewer clumps and degraded more PET than the nonglycosylated protein. The improved stability and activity marks a big step toward optimizing the enzyme for commercial recycling of PET, Gross says.