User:Lllcrush/PETase Enzyme

PETase （3.1.1.101）is an amazing plastic-eating bacterium called Ideonella sakaiensis, reported in 2016 by a team of researchers from Japan, The paper was published in Science with the title "A bacterium that degrades and assimilates poly(ethylene terephthalate)."

History
The results show that the bacteria can attach to the surface of PET, secrete a new PET hydrolase to break the PET into small pieces, and then transport the product into the body for further "digestion", eventually converted into two relatively simple organic compounds, ethylene glycol and terephthalic acid. This finding is a major boost to the development of PET biodegradation engineering. First, a microorganism that can grow on PET as an energy source has been isolated, and more importantly, a powerful PET hydrolase has finally been developed.

Reactions
PET enzyme can degrade PET plastic into its monomer -2- hydroxyethyl terephthalic acid (MHET) molecule. MHET in bacteria is further degraded by MHET enzyme (MHETase) to hydroxyethyl terephthalic acid, which is then decomposed into environmentally friendly terephthalic acid and ethylene glycol in water, and can be used by other bacteria to produce carbon dioxide and water.

The reaction formula catalyzed by PET enzyme can be simply expressed as:

(PET)n + H2O departure (ethylene terephthalate)n-1 + MHET

Structure
Until 2018, several stereoscopic structures have been resolved, including 5XH3, 5XH2, 5XG0, 5XFZ, 5XFY, 5YNS, 5XJH, etc.



Function
From the perspective of overall protein structure comparison, PETase is very similar to other PET decomposers previously reported, except for two structural features of the active region. First, PET hydrolase has an extra pair of disulfide bonds than other enzyme species, which is crucial for the stability of the structure of the active center catalytic terpolymer. After the mutation, the enzyme activity is greatly reduced. Second, one of the amino acids W156 side chains in the substrate binding region has different configurations, and W156 is held in a certain direction (called the B-configuration) when the substrate is bound and provides an important force for substrate binding. This W156 site is conserved among all PET catabolizes. However, in other less active enzymes, W156 adopts the C configuration, which is not conducive to substrate binding. Further analysis of the cause of W156 swing in PET hydrolase revealed that the adjacent S185 site was histamine acid in other enzymes, and the stacking force between histamine acid and W156 fixed the side chain of W156 in the C configuration. If the S185 of PET hydrolase was mutated to histamine acid, the hydrolysis efficiency of PET was significantly reduced. These results not only for the research of PET hydrolase has important guiding significance, for research has important enzymology, namely amino acids may show different features in different configurations, active area outside of the amino acids can also affect the combination and the enzyme activity and parse the high-resolution mechanism of protein crystal structure for the further research is indispensable.

Problem
Although PETase has a natural ability to degrade some semi-crystalline forms of PET, it is unstable at temperatures above 40 ° C. This results in a low rate of depolymerization. Another heat-resistant enzyme needs to be developed to match it.

Reference
1.Chun-Chi Chen, Xu Han, Tzu-Ping Ko, Weidong Liu, Rey-Ting Guo. (2018). Structural studies reveal the molecular mechanism of PETase. PMID: 30048043. DOI: 10.1111/febs.14612. https://doi.org/10.1111/febs.14612

2. Mindy Weisberger. 2018-04-17. Lab 'Accident' Becomes Mutant Enzyme That Devours Plastic. https://www.livescience.com/62328-plastic-eating-enzyme.html

3. Harry P. Austin, Mark D. Allen, Bryon S. Donohoe. 2018-04-17. Characterization and engineering of a plastic-degrading aromatic polyesterase. 115 (19) E4350-E4357. https://doi.org/10.1073/pnas.1718804115

Yoshida S., Hiraga K., Takehana T., Taniguchi I., Yamaji H., Maeda Y., Toyohara K., Miyamoto K., Kimura Y., Oda K., A bacterium that degrades and assimilates poly(ethylene terephthalate). Science 351, 1196–1199 (2016). https://doi.org/10.1126/science.aad6359