PETase

The first PETase was discovered in 2016 from Ideonella sakaiensis strain 201-F6 bacteria found from sludge samples collected close to a Japanese PET bottle recycling site.[1][4] Other types of PET degrading hydrolases have been known before this discovery.[2] These include hydrolases such as: lipases, esterases, and cutinases.[5] Discoveries of polyester degrading enzymes date at least as far back as 1975 (α-chymotrypsin)[6] and 1977 (lipase) for example.[7]

PET plastic was put into widespread use in the 1970s and it has been suggested that PETases in bacteria evolved only recently.[2] PETase may have had past enzymatic activity associated with degradation of a waxy coating on plants.[8]

As of April 2019, there were 17 known three-dimensional crystal structures of PETases: 6QGC, 6ILX, 6ILW, 5YFE, 6EQD, 6EQE, 6EQF, 6EQG, 6EQH, 6ANE, 5XJH, 5YNS, 5XFY, 5XFZ, 5XG0, 5XH2 and 5XH3.

PETase exhibits shared qualities with both lipases and cutinases in that it possesses an α/β-hydrolase fold; although, the active-site cleft observed in PETase is more open than in cutinases.[2] The Ideonella sakaiensis PETase is similar to dienelactone hydrolase, according to Pfam. According to ESTHER, it falls into the Polyesterase-lipase-cutinase family.

There are approximately 69 PETase-like enzymes comprising a variety of diverse organisms, and there are two classifications of these enzymes including type I and type II. It is suggested that 57 enzymes fall into the type I category whereas the rest fall into the type II group, including the PETase enzyme found in the Ideonella sakaiensis. Within all 69 PETase-like enzymes, there exists the same three residues within the active site, suggesting that the catalytic mechanism is the same in all forms of PETase-like enzymes.[9]

• 
  Surface of the PETase double mutant (R103G and S131A) with HEMT (1-(2-hydroxyethyl) 4-methyl terephthalate) bound to its active site. HEMT is an analogue of MHET, and has an additional methanol esterified to it. PDBID: 5XH3.
• 
  Ribbon diagram of PETase with three residues Ser160, Asp206, and His237. The catalytic triad is represented by cyan-colored sticks. The active site is shown in orange to represent stimulation by a 2-HE(MHET)₄ molecule.[9]

In 2018 scientists from the University of Portsmouth with the collaboration of the National Renewable Energy Laboratory of the United States Department of Energy developed a mutant of this PETase that degrades PET faster than the one in its natural state. In this study it was also shown that PETases can degrade polyethylene 2,5-furandicarboxylate (PEF).[2][10]

PETase and MHETase reaction pathway.[11]

In I. sakaiensis, the resultant MHET is further broken down by the action of MHETase enzyme to terephthalic acid and ethylene glycol.[1] Laboratory experiments showed that chimeric proteins that artificially link a MHETase and a PETase outperform similar mixtures of free enzymes.[12]

Look up petase in Wiktionary, the free dictionary.

• Organisms breaking down plastic
• Galleria mellonella, a caterpillar that can digest polyethylene.
• Aspergillus tubingensis, a fungus that can digest polyurethane.
• Pestalotiopsis microspora, an endophytic fungus species able to break down polyurethane.
• cutinase, an esterase enzyme of similar geometric shape