PETase enzyme

Abstract

Polyethylene terephthalate is one of the most popular types of plastic and is used to make beverage containers and man-made fiber. Researchers are therefore looking for ways to recycle PET without harming the environment. In 2016, Japanese microbiologists examining soil near a PET plant found the bacterium Ideonella sakaiensis (now renamed Piscinibacter sakaiensis 201-F6), which hydrolyzes it. Using special enzymes, the microorganism breaks down PET into low-toxic terephthalic acid and ethylene glycol. In six weeks, the bacteria were able to process the 0.2-millimeter-thick polymer film.

One of the enzymes of I. sakaiensis, PETase, "triggers" the PET degradation process and cleaves the polymer into monomeric links.

PETase belongs to the α/β-hydrolase superfamily with highly conserved structures including a central twisted β-sheet (α3) formed by 9 mixed β strands and surrounded by seven α-helices and a Gly-X-Ser-X-Gly motif. Ser160, Asp206 and His237 form a catalytic triad, and two disulfide bonds (C203-C239 and C237-C289) were also identified. Site-directed mutation analysis revealed that DS1, W156, S185 and Y58 may play a crucial role in PET degradation [1]. Moreover, W156 residues adjacent to the active site have different conformations, including "A", "B" and "C" conformers, which are important for substrate binding and product release. Interestingly, the enzyme-substrate interactions of PETase are largely identical to those of ICCG, with the most notable change being that the aromatic component of the two bound ligands deviates by about 30° [2].