Low modification of PETase enhances its activity toward degrading PET: Effect of conjugate monomer property

Abstract

Polyethylene terephthalate is one of the most widely used synthetic plastics. The accumulation of abandoned PET has brought an environmental problem. A recently reported PET hydrolase, PETase, displays an efficient decomposition to PET. Herein, we synthesized four PETase conjugates by modifying four types of monomers onto PETase, which were hydrophobic tert-butyl methacrylate (TBMA), hydrophilic hydroxyethyl methacrylate (HEMA), positively charged 2-(dimethylamino)ethyl methacrylate (DMAEMA), and negatively charged methacrylic acid (MA). Despite the low modification with an average number of 3–5 monomers on each enzyme molecule, all the PETase conjugates exhibited improved enzyme activity, and thermal and pH stability. Particularly, the catalytic efficiency (kcat/Km) of TBMA-/DMAEMA-PETase toward bis-2(hydroxyethyl) terephthalate (BHET) increased 1.4 and 1.6-fold as compared with PETase. Characterizations by fluorescence and circular dichroism spectroscopy unraveled that the modification induced the structural transformations, including compact overall structure and opened substrate-binding pocket, which were in favor of the enhanced catalytic performance. Biodegradation against PET films by TBMA-/DMAEMA-PETase were 4.69 and 3.26-fold higher than PETase. The different catalytic performances of the enzyme conjugates for BHET and PET are considered due to the different interactions of the conjugates with the different substrates. The work demonstrated that the low modifications with hydrophobic and hydrophilic monomers were both effective in improving the catalytic performance toward PET degradation, especially for the hydrophobic and positively charged monomers.