Plastic bioconversion: Reaction mechanism of PETases

The enzyme IsPETase can efficiently degrade polyethylene terephthalate (PET) at room temperature and is an attractive method of plastic bioconversion. Based on mutagenesis experiments on IsPETase, we propose a physical model which predicts that its reaction mechanism can be described by the Michaelis-Menten model with a catalytic efficiency of K_a∙k₂, where K_a is the association constant of substrate binding and k₂ is the rate constant to form the acyl-enzyme intermediate. This model verifies the assumption of Michaelis-Menten kinetics in previous studies on PETases and has novel applications in deriving the enzyme activity using computational molecular dockings. By computationally docking bis-(2-hydroxyethyl) terephthalic acid (BHET) on the surface of IsPETase mutants, we studied the catalytic effects of various side chains and observed that their predicted activities are consistent with experimental data, with a correlation coefficient in the range of 0.79∼0.88. Based on this study, our model presents an analytical interpretation for the reaction mechanism of PETases and provides an efficient method for computing their catalytic efficiency for identifying enzymes with a better catalytic performance from numerous protein sequences in open databases.