PETase

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PETase
PETase 5XH3 with HEMT-cartoon.png
Identifiers
EC number3.1.1.101
Alt. namesPET hydrolase, poly(ethylene terephthalate) hydrolase
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum

PETases are an esterase class of enzymes that catalyze the hydrolysis of polyethylene terephthalate (PET) plastic to monomeric mono-2-hydroxyethyl terephthalate (MHET). The idealized chemical reaction is (where n is the number of monomers in the polymer chain):[1]

(ethylene terephthalate)n + H2O → (ethylene terephthalate)n-1 + MHET

Trace amount of the PET breaks down to bis(2-hydroxyethyl) terephthalate (BHET). PETases can also break down PEF-plastic (polyethylene-2,5-furandicarboxylate), which is a bioderived PET replacement. PETases can't catalyze the hydrolysis of aliphatic polyesters like polybutylene succinate or polylactic acid.[2]

Non-enzymatic natural degradation of PET will take hundreds of years, but PETases can degrade PET in matter of days.[3]

History[edit]

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]

MHET breakdown in I. sakaiensis[edit]

PETase and MHETase reaction pathway.[9]

MHET is broken down in I. sakaiensis by the action of MHETase enzyme to terephthalic acid and ethylene glycol.[1]

Structure[edit]

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.[10]

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.[11]

Mutations[edit]

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]

See also[edit]

References[edit]

  1. ^ a b c Yoshida S, Hiraga K, Takehana T, Taniguchi I, Yamaji H, Maeda Y, et al. (March 2016). "A bacterium that degrades and assimilates poly(ethylene terephthalate)". Science. 351 (6278): 1196–9. doi:10.1126/science.aad6359. PMID 26965627. Lay summary (PDF) (2016-03-30).
  2. ^ a b c d Austin HP, Allen MD, Donohoe BS, Rorrer NA, Kearns FL, Silveira RL, et al. (May 2018). "Characterization and engineering of a plastic-degrading aromatic polyesterase". Proceedings of the National Academy of Sciences of the United States of America. 115 (19): E4350–E4357. doi:10.1073/pnas.1718804115. PMC 5948967. PMID 29666242.
  3. ^ Dockrill, Peter. "Scientists Have Accidentally Created a Mutant Enzyme That Eats Plastic Waste". ScienceAlert. Retrieved 2018-11-27.
  4. ^ Tanasupawat S, Takehana T, Yoshida S, Hiraga K, Oda K (August 2016). "Ideonella sakaiensis sp. nov., isolated from a microbial consortium that degrades poly(ethylene terephthalate)". International Journal of Systematic and Evolutionary Microbiology. 66 (8): 2813–8. doi:10.1099/ijsem.0.001058. PMID 27045688.
  5. ^ Han X, Liu W, Huang JW, Ma J, Zheng Y, Ko TP, et al. (December 2017). "Structural insight into catalytic mechanism of PET hydrolase". Nature Communications. 8 (1): 2106. doi:10.1038/s41467-017-02255-z. PMC 5727383. PMID 29235460.
  6. ^ Tabushi I, Yamada H, Matsuzaki H, Furukawa J (August 1975). "Polyester readily hydrolyzable by chymotrypsin". Journal of Polymer Science: Polymer Letters Edition. 13 (8): 447–450. doi:10.1002/pol.1975.130130801.
  7. ^ Tokiwa Y, Suzuki T (November 1977). "Hydrolysis of polyesters by lipases". Nature. 270 (5632): 76–8. doi:10.1038/270076a0. PMID 927523.
  8. ^ "Lab 'Accident' Becomes Mutant Enzyme That Devours Plastic". Live Science. Retrieved 2018-11-27.
  9. ^ Allison Chan (2016). "The Future of Bacteria Cleaning Our Plastic Waste" (PDF).
  10. ^ Austin HP, Allen MD, Donohoe BS, Rorrer NA, Kearns FL, Silveira RL, et al. (May 2018). "Characterization and engineering of a plastic-degrading aromatic polyesterase". Proceedings of the National Academy of Sciences of the United States of America. 115 (19): E4350–E4357. doi:10.1073/pnas.1718804115. PMC 5948967. PMID 29666242.
  11. ^ a b Joo S, Cho IJ, Seo H, Son HF, Sagong HY, Shin TJ, et al. (January 2018). "Structural insight into molecular mechanism of poly(ethylene terephthalate) degradation". Nature Communications. 9 (1): 382. doi:10.1038/s41467-018-02881-1. PMC 5785972. PMID 29374183.