View source for PETase

{{Short description|Class of enzymes}}
{{Infobox enzyme
|name = PETase
|AltNames = PET hydrolase, poly(ethylene terephthalate) hydrolase
|image =PETase_5XH3_with_HEMT-cartoon.png
|caption = ''I. sakaiensis'' PETase ({{UniProt|A0A0K8P6T7}}) in complex with HEMT, a PET analogue ({{PDB|5XH3}}).
|EC_number = 3.1.1.101
}}
'''PETases''' are an [[esterase]] class of [[enzyme]]s that [[Catalysis|catalyze]] the breakdown (via [[hydrolysis]]) of [[polyethylene terephthalate]] (PET) plastic to [[monomer]]ic [[2-Hydroxyethyl terephthalic acid|mono-2-hydroxyethyl terephthalate]] (MHET). The idealized chemical reaction is:
:(ethylene terephthalate)<sub>''n''</sub> + H<sub>2</sub>O → (ethylene terephthalate)<sub>''n''-1</sub> + MHET,
where ''n'' is the number of [[monomer]]s in the [[polymer]] chain, though a trace amount of the PET breaks down instead to [[Bis(2-Hydroxyethyl) terephthalate|bis(2-hydroxyethyl) terephthalate]] (BHET).<ref name="Yoshida 2016" /> PETases can also break down PEF-plastic ([[Polyethylene 2,5-furandicarboxylate|polyethylene-2,5-furandicarboxylate]]), which is a bioderived PET replacement, into the analogous {{abbr|MHEF|mono-2-hydroxyethyl furanoate}}. PETases can't catalyze the hydrolysis of [[Aliphatic compound|aliphatic]] [[polyester]]s like [[polybutylene succinate]] or [[polylactic acid]].<ref name="Austin 2018">{{cite journal | vauthors = 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 | display-authors = 6 | title = Characterization and engineering of a plastic-degrading aromatic polyesterase | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 115 | issue = 19 | pages = E4350–E4357 | date = May 2018 | pmid = 29666242 | pmc = 5948967 | doi = 10.1073/pnas.1718804115 | bibcode = 2018PNAS..115E4350A | doi-access = free}}</ref>
Whereas the degradation of PET by natural (non-enzymatic) means  will take hundreds of years,  PETases can degrade it in a matter of days.<ref>{{Cite news|url=https://www.sciencealert.com/scientists-accidentally-engineered-mutant-enzyme-eats-through-plastic-pet-petase-pollution|title=Scientists Have Accidentally Created a Mutant Enzyme That Eats Plastic Waste|last=Dockrill|first=Peter|work=ScienceAlert|access-date=2018-11-27|language=en-gb}}</ref>
==History==
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.<ref name="Yoshida 2016" /><ref>{{cite journal | vauthors = Tanasupawat S, Takehana T, Yoshida S, Hiraga K, Oda K | title = Ideonella sakaiensis sp. nov., isolated from a microbial consortium that degrades poly(ethylene terephthalate) | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 66 | issue = 8 | pages = 2813–8 | date = August 2016 | pmid = 27045688 | doi = 10.1099/ijsem.0.001058 | doi-access = free }}</ref> There were other types of [[hydrolase]]s previously known to degrade PET,<ref name="Austin 2018"/> including lipases, esterases, and cutinases.<ref name="Han 2017">{{cite journal | vauthors = Han X, Liu W, Huang JW, Ma J, Zheng Y, Ko TP, Xu L, Cheng YS, Chen CC, Guo RT | display-authors = 6 | title = Structural insight into catalytic mechanism of PET hydrolase | language = En | journal = Nature Communications | volume = 8 | issue = 1 | pages = 2106 | date = December 2017 | pmid = 29235460 | pmc = 5727383 | doi = 10.1038/s41467-017-02255-z| bibcode = 2017NatCo...8.2106H }}</ref> For comparison, enzymes that degrade [[polyester]] have been known to exist at least as far back as 1975 (in the case of α-[[chymotrypsin]])<ref>{{cite journal |last1=Tabushi|first1=Iwao |last2=Yamada|first2=Hidenori |last3=Matsuzaki|first3=Hidetaka |last4=Furukawa|first4=Junji | name-list-style = vanc |date=August 1975 |title=Polyester readily hydrolyzable by chymotrypsin  |journal=Journal of Polymer Science: Polymer Letters Edition |volume=13|issue=8|pages=447–450|doi=10.1002/pol.1975.130130801|bibcode=1975JPoSL..13..447T }}</ref> and 1977 ([[lipase]]).<ref>{{cite journal | vauthors = Tokiwa Y, Suzuki T | title = Hydrolysis of polyesters by lipases | journal = Nature | volume = 270 | issue = 5632 | pages = 76–8 | date = November 1977 | pmid = 927523 | doi = 10.1038/270076a0 | bibcode = 1977Natur.270...76T | s2cid = 4145159}}</ref>
PET plastic came into widespread use in the 1970s and it has been suggested that PETases in bacteria evolved only recently.<ref name="Austin 2018" /> PETase may have had past enzymatic activity associated with degradation of a waxy coating on plants.<ref>{{Cite news|url=https://www.livescience.com/62328-plastic-eating-enzyme.html|title=Lab 'Accident' Becomes Mutant Enzyme That Devours Plastic|work=Live Science|access-date=2018-11-27}}</ref>
== Structure ==
As of April 2019, there were 17 known three-dimensional crystal structures of PETases: [https://www.rcsb.org/structure/6QGC 6QGC], [https://www.rcsb.org/structure/6ILX 6ILX], [https://www.rcsb.org/structure/6ILW 6ILW], [https://www.rcsb.org/structure/5YFE 5YFE], [https://www.rcsb.org/structure/6EQD 6EQD], [https://www.rcsb.org/structure/6EQE 6EQE], [https://www.rcsb.org/structure/6EQF 6EQF], [https://www.rcsb.org/structure/6EQG 6EQG], [https://www.rcsb.org/structure/6EQH 6EQH], [https://www.rcsb.org/structure/6ANE 6ANE], [https://www.rcsb.org/structure/5XJH 5XJH], [https://www.rcsb.org/structure/5YNS 5YNS], [https://www.rcsb.org/structure/5XFY 5XFY], [https://www.rcsb.org/structure/5XFZ 5XFZ], [https://www.rcsb.org/structure/5XG0 5XG0], [https://www.rcsb.org/structure/5XH2 5XH2] and [https://www.rcsb.org/structure/5XH3 5XH3].
PETase exhibits shared qualities with both lipases and cutinases in that it possesses an [[alpha/beta hydrolase superfamily|α/β-hydrolase]] fold; although, the active-site cleft observed in PETase is more open than in cutinases.<ref name="Austin 2018" /> 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.<ref name="Joo 2018">{{cite journal | vauthors = Joo S, Cho IJ, Seo H, Son HF, Sagong HY, Shin TJ, Choi SY, Lee SY, Kim KJ | display-authors = 6 | title = Structural insight into molecular mechanism of poly(ethylene terephthalate) degradation | language = En | journal = Nature Communications | volume = 9 | issue = 1 | pages = 382 | date = January 2018 | pmid = 29374183 | pmc = 5785972 | doi = 10.1038/s41467-018-02881-1 | bibcode = 2018NatCo...9..382J }}</ref>
<gallery mode="packed" heights="230px" style="text-align:left">
PETase 5XH3 with HEMT-surface.png|Surface of the PETase double [[mutant]] ([[Arginine|R]]103[[Glycine|G]] and [[Serine|S]]131[[Alanine|A]]) with HEMT (1-(2-hydroxyethyl) 4-methyl terephthalate) bound to its [[active site]]. HEMT is an analogue of MHET, and has an additional [[methanol]] [[ester]]ified to it. PDBID: 5XH3.
PETase active site.png|[[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)<sub>4</sub> molecule.<ref name="Joo 2018"/>
</gallery>
==Mutations==
The discovery of PETase from ''I. sakaiensis'' provides a potential solution to the world’s amassing plastic; however, naturally occurring enzymes are limited in their degradation abilities due to instability, low activity, and expression levels, which ultimately drive the need for improvement if they are to be used for large-scale industrial applications.<ref name="Qi-2021">{{Cite journal |last1=Qi |first1=Xinhua |last2=Yan |first2=Wenlong |last3=Cao |first3=Zhibei |last4=Ding |first4=Mingzhu |last5=Yuan |first5=Yingjin |date=2021-12-26 |title=Current Advances in the Biodegradation and Bioconversion of Polyethylene Terephthalate |journal=Microorganisms |language=en |volume=10 |issue=1 |pages=39 |doi=10.3390/microorganisms10010039 |issn=2076-2607 |pmc=8779501 |pmid=35056486 |doi-access=free }}</ref> The majority of strategies implement [[site-directed mutagenesis]] to create an improved version, known as a variant or mutant, of the enzyme. One variant increased the activity of PETase by 22.4% by replacing the arginine with alanine in the amino acid chain at the 280th position.<ref name="Urbanek-2021">{{Cite journal |last1=Urbanek |first1=Aneta K. |last2=Kosiorowska |first2=Katarzyna E. |last3=Mirończuk |first3=Aleksandra M. |date=2021-11-30 |title=Current Knowledge on Polyethylene Terephthalate Degradation by Genetically Modified Microorganisms |journal=Frontiers in Bioengineering and Biotechnology |volume=9 |doi=10.3389/fbioe.2021.771133 |issn=2296-4185 |pmc=8669999 |pmid=34917598 |doi-access=free }}</ref> Similarly, a double mutant was created to constrict the active site and became 4.13% more active than the wildtype.<ref>{{Cite journal |last1=Austin |first1=Harry P. |last2=Allen |first2=Mark D. |last3=Donohoe |first3=Bryon S. |last4=Rorrer |first4=Nicholas A. |last5=Kearns |first5=Fiona L. |last6=Silveira |first6=Rodrigo L. |last7=Pollard |first7=Benjamin C. |last8=Dominick |first8=Graham |last9=Duman |first9=Ramona |last10=El Omari |first10=Kamel |last11=Mykhaylyk |first11=Vitaliy |last12=Wagner |first12=Armin |last13=Michener |first13=William E. |last14=Amore |first14=Antonella |last15=Skaf |first15=Munir S. |date=2018-05-08 |title=Characterization and engineering of a plastic-degrading aromatic polyesterase |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=19 |pages=E4350–E4357 |doi=10.1073/pnas.1718804115 |issn=0027-8424 |pmc=5948967 |pmid=29666242 |bibcode=2018PNAS..115E4350A |doi-access=free }}</ref> Comparatively, two other double mutants created extra hydrogen bonds that improved the stability of PETase. Other successful approaches to improving PETase stability include adding Ca<sup>2+</sup> or Mg<sup>2+</sup>, [[disulfide bonds]] and [[Salt bridge (protein and supramolecular)|salt bridges]] as well as [[glycosylation]].<ref name="Qi-2021" /> For thermal stability, another double mutant displayed an increase in comparison to the wild type.<ref name="Urbanek-2021" /> Moreover, the β1-β2 connecting loop of the enzyme may also be a future target for improved thermal stability due to its flexibility and distance from the active site.<ref>{{Cite journal |last1=da Costa |first1=Clauber Henrique Souza |last2=dos Santos |first2=Alberto M. |last3=Alves |first3=Cláudio Nahum |last4=Martí |first4=Sérgio |last5=Moliner |first5=Vicent |last6=Santana |first6=Kauê |last7=Lameira |first7=Jerônimo |date=October 2021 |title=Assessment of the PETase conformational changes induced by poly(ethylene terephthalate) binding |url=https://onlinelibrary.wiley.com/doi/10.1002/prot.26155 |journal=Proteins: Structure, Function, and Bioinformatics |language=en |volume=89 |issue=10 |pages=1340–1352 |doi=10.1002/prot.26155 |pmid=34075621 |s2cid=233620229 |issn=0887-3585}}</ref>
==Biological pathway {{anchor|MHET breakdown in I. sakaiensis}}==
[[File:Plastic Breakdown by PETase.png|thumb|PETase and MHETase reaction pathway.<ref>{{Cite web|url=https://cloudfront.escholarship.org/dist/prd/content/qt7xb0c7hr/qt7xb0c7hr.pdf|title=The Future of Bacteria Cleaning Our Plastic Waste|last=Allison Chan|date=2016}}</ref>]]
In ''I. sakaiensis'', the resultant MHET is further broken down by the action of [[MHETase]] enzyme to [[terephthalic acid]] and [[ethylene glycol]].<ref name="Yoshida 2016">{{cite journal | vauthors = Yoshida S, Hiraga K, Takehana T, Taniguchi I, Yamaji H, Maeda Y, Toyohara K, Miyamoto K, Kimura Y, Oda K | display-authors = 6 | title = A bacterium that degrades and assimilates poly(ethylene terephthalate) | journal = Science | volume = 351 | issue = 6278 | pages = 1196–9 | date = March 2016 | pmid = 26965627 | doi = 10.1126/science.aad6359 | bibcode = 2016Sci...351.1196Y | s2cid = 31146235}}
* {{cite press release |date=2016-03-30 |title=Discovery of a Bacterium that Degrades and Assimilates Poly(ethylene terephthalate) could Serve as a Degradation and/or Fermentation Platform for Biological Recycling of PET Waste Products |website=Kyoto Institute of Technology |url=https://www.keio.ac.jp/en/press_releases/2016/cb96u90000005501-att/160330_2.pdf}}</ref> Laboratory experiments showed that chimeric proteins that artificially link a MHETase and a PETase outperform similar mixtures of free enzymes.<ref name="Knott 2020">{{cite journal | vauthors = Knott BC, Erickson E, Allen MD, Gado JE, Graham R, Kearns FL, Pardo I, Topuzlu E, Anderson JJ, Austin HP, Dominick G, Johnson CW, Rorrer NA, Szostkiewicz CJ, Copié V, Payne CM, Woodcock HL, Donohoe BS, Beckham GT, McGeehan JE | display-authors = 6 | title = Characterization and engineering of a two-enzyme system for plastics depolymerization. | journal = Proc Natl Acad Sci U S A | volume = 117 | issue = 41 | pages = 25476–25485 | date = Oct 2020 | pmid = 32989159 | doi = 10.1073/pnas.2006753117 | pmc = 7568301 | bibcode = 2020PNAS..11725476K | doi-access = free}}</ref>
== See also ==
{{wiktionary}}
*[[Plastivore]]
*''[[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
== References ==
{{Reflist}}
{{Esterases}}
[[Category:Hydrolases]]
[[Category:Recycling]]