SUMMARY: There is a bacterium that makes PETase (an enzyme that can digest PET plastic). Researchers in this paper took this PETase enzyme, modified it slightly, and made it better. The modifications were to add in parts that were commonly seen in other enzymes such as cutinases and lipases; these changes made the active site of the PETase bigger. This modified PETase only works on PET, not on other types of plastic (PLA and PBS). The reason no one uses enzymes to break down plastic is due to cost. If we are able to create more efficient enzymes, perhaps this could be a viable way to dispose of our plastic garbage.
LESSON COMMENT: Enzyme specificity is an important concept in biology that’s covered in this article. Students can look up the different molecular structures of the various plastics as well to see how similar plastics can be (this is why PETase only really works on PET). This is also a good article to talk about the difference between aliphatic and aromatic structures. Biology textbooks often talk about the structural differences between starch and cellulose, the specificity of amylase, and using this as an example of enzyme specificity. In the discussion section, the fourth paragraph talks about the similar problems between digesting plastic and digesting polysaccharides. I would use this to expand students’ exposure to examples of enzyme specificity and have them brainstorm other examples.
Austin, H. P., Allen, M. D., Donohoe, B. S., Rorrer, N. A., Kearns, F. L., Silveira, R. L., . . . Beckham, G. T. (2018). Characterization and engineering of a plastic-degrading aromatic polyesterase. Proceedings of the National Academy of Sciences,115(19). doi:10.1073/pnas.1718804115