Substrate Inhibition of the Highly Efficient PET Hydrolase

Polyethylene terephthalate (PET) is one of the most abundant polyester materials used in daily life and it is also one of the culprits of environmental pollution. ICCG (F243I/D238C/S283C/Y127G) is a quadruple mutant of leaf-branch compost cutinase (LCC) displaying outstanding performance in hydrolyzing PET and holding a great potential in further applications. Substrate concentration is one of the important factors affecting the catalytic degradation efficiency. The conventional fast equilibrium theory holds that the degradation rate reaches the maximum and tends to be stable with the increase of substrate concentration, however, in practice, too much substrate will inhibit the catalytic reaction. In this study, the substrate inhibitory effect of PET plastic particles with different particle sizes on ICCG was evaluated. Combined with kinetic constant analysis, the optimal PET particle size was determined to be 300 μm. Meanwhile, several mutants (Y95K, M166S and H218S) of ICCG were obtained by site-directed mutagenesis. The effect of substrate concentration on mutant was studied under the condition of optimal reaction particle size. This study provides a strategy for obtaining high-efficiency PET degradation mutants and a new possibility of environmentally friendly plastic degradation.