Overcoming catalytic barriers to reprogram acyltransferases for bis(2-hydroxyethyl) terephthalate hydrolysis.

Abstract

The extensive use of polyethylene terephthalate (PET) has resulted in severe environmental pollution and ecological stress. Despite advances in PET recycling, current processes struggle to achieve high product value, as the complete conversion to terephthalic acid remains energetically demanding and economically inefficient. The catalytic promiscuity inherent in natural enzyme evolution holds great promise for providing novel candidates to accelerate PET biodegradation and upcycling. Herein, we report for the first time that the acyltransferase metA from Mycobacterium tuberculosis (MtMetA) catalyzes the conversion of bis(2-hydroxyethyl) terephthalate (BHET), an intermediate of PET hydrolysis, into the high-value monomer mono(2-hydroxyethyl) terephthalate (MHET). Guided by molecular dynamics (MD) simulations, we applied a catalytic barrier-minimization strategy to optimize the active-site environment of MtMetA, yielding engineered variants, notably ΔBarrier2 and ΔBarrier3. Specifically, ΔBarrier2 achieved a 3.1-fold increase in MHET yield, while ΔBarrier3 demonstrated a 3.2-fold enhancement in catalytic efficiency (kcat/KM) relative to the wild-type. The truncated MtMetA variants also exhibited enhanced robustness, showing improved thermostability (3.5-fold increase in residual activity at 60 °C for ΔBarrier3), as well as higher tolerance to metal ions and organic solvents. Specifically, ΔBarrier2 displayed a 7.2-fold increase in product yield in Ca2+-containing systems, while ΔBarrier3 retained 2.3-fold higher residual activity in the presence of 50 % (v/v) isopropanol. MD simulations revealed that an enlarged active pocket and a shortened nucleophilic attack distance synergistically govern the enhanced catalytic activity and robustness. This work expands the enzymatic toolbox for PET recycling and targeted BHET degradation, advancing sustainable plastic waste management through biocatalytic innovations.