Characterization and engineering of a plastic-degrading aromatic polyesterase

Area of Science:

• Biochemistry
• Environmental Science
• Polymer Science

Background:

• Poly(ethylene terephthalate) (PET) is a widely used synthetic polymer accumulating in the environment due to its resistance to biodegradation.
• Ideonella sakaiensis 201-F6 is a bacterium capable of degrading PET using a secreted enzyme called PETase.

Purpose of the Study:

• To elucidate the X-ray crystal structure of PETase at 0.92 Å resolution.
• To investigate the structure-activity relationship of PETase for enhanced PET degradation.
• To assess PETase activity against other polyesters like polyethylene-2,5-furandicarboxylate (PEF).

Main Methods:

• X-ray crystallography to determine the 3D structure of PETase.
• Site-directed mutagenesis to modify the active-site cleft of PETase.
• Enzymatic assays to measure the degradation rates of PET and PEF.

Main Results:

• The crystal structure revealed PETase shares features with cutinases and lipases, possessing an open active-site cleft.
• Mutating two active-site residues to mimic cutinase conserved amino acids surprisingly improved PET degradation efficiency.
• PETase demonstrated degradation of the aromatic polyester PEF but not aliphatic polyesters, indicating it is an aromatic polyesterase.

Conclusions:

• PETase is not fully optimized for crystalline PET degradation, presenting opportunities for protein engineering.
• Further structural and functional studies are needed to enhance PETase's biodegradation capabilities for synthetic polyesters.
• PETase shows promise for the biodegradation of PET and potentially other aromatic polyesters like PEF.