PETase

PETase
Identifiers
EC number 3.1.1.101
Alt. names PET hydrolase, poly(ethylene terephthalate) hydrolase
Databases
IntEnz IntEnz view
BRENDA BRENDA entry
ExPASy NiceZyme view
KEGG KEGG entry
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum

PETases are an esterase class of enzymes that catalyze the hydrolysis of 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]

History

The first PETase enzyme 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][3] Other types of PET degrading hydolases have been known before this discovery.[2] Discoveries of polyester degrading enzymes date at least as far back as 1975 (α-chymotrypsin)[4] and 1977 (lipase) for example.[5] PET plastic was put into widespread use in the 1970s and it has been suggested that PETases in bacteria evolved only recently.[2]

MHET breakdown in I. sakaiensis

MHET is broken down in I. sakaiensis by the action of MHETase enzyme to terephthalic acid and ethylene glycol. These are environmentally harmless as they are broken down further to produce carbon dioxide and water.[1]

Structure

Surface of the PETase double mutant (R103G and S131A) with HEMT (1-(2-hydroxyethyl) 4-methyl terephthalate) bound to its active site. HEMT is a close analogue of MHET. HEMT has an additional methanol esterified to it. MHET binds to the site in a similar manner. PDBID: 5XH3.

As of April 2018, there were 13 known three-dimensional crystal structures of PETases: 6EQD, 6EQE, 6EQF, 6EQG, 6EQH, 6ANE, 5XJH, 5YNS, 5XFY, 5XFZ, 5XG0, 5XH2 and 5XH3.

Animations and images

PET MHET after PETase

enzyme breakdown

from PET

 animation of

breakdown from

PET to ethylene glycol

and terephthalic acid

end result of

breakdown

 further breakdown

Mutations

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

References

  1. 1 2 3 Yoshida S, Hiraga K, Takehana T, Taniguchi I, Yamaji H, Maeda Y, Toyohara K, Miyamoto K, Kimura Y, Oda K (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. 1 2 3 4 Austin HP, Allen MD, Donohoe BS, Rorrer NA, Kearns FL, Silveira RL, Pollard BC, Dominick G, Duman R, El Omari K, Mykhaylyk V, Wagner A, Michener WE, Amore A, Skaf MS, Crowley MF, Thorne AW, Johnson CW, Woodcock HL, McGeehan JE, Beckham GT (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. PMID 29666242.
  3. ↑ 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.
  4. ↑ 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.
  5. ↑ Tokiwa Y, Suzuki T (November 1977). "Hydrolysis of polyesters by lipases". Nature. 270 (5632): 76–8. doi:10.1038/270076a0. PMID 927523.
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