Valuable Compounds from Pollutants: Converting PET into Enantiopure Alanine

The enzymatic depolymerization of single-use plastic products, primarily made from poly(ethylene terephthalate) (PET), is now a reality. Herein, we report the development of an innovative tandem system process that uses engineered enzymes and Escherichia coli strains to depolymerize PET and convert the resulting products into enantiomers of alanine, useful amino acids, and starting point for further valorization processes. A biosynthetic pathway has been generated, consisting of twelve enzymes derived from four different microorganisms. This pathway has been optimized using recombinant proteins and whole-cells that harbor different modules of the pathway. Specifically, the S101N/F243T-ΔLCC variant was selected to degrade PET into terephthalic acid (TPA) and ethylene glycol also at 37 °C, a temperature compatible with the E. coli RARE strain. A recombinant E. coli strain catalyzed the subsequent conversion of TPA into 2-pyrone-4,6-dicarboxylic acid, which is then transformed into pyruvate by recombinant enzymes to prevent depletion of pyruvate due to cellular catabolism. Finally, pyruvate is enzymatically aminated to enantiopure d- or l-alanine. We successfully converted postconsumer PET waste into d- and l-alanine, with an overall yield of 50 mg/170 mg PET, demonstrating that the bioconversion of selected plastics into valuable biomolecules via an eco-friendly process is feasible.