Team:ASTWS-China/Contribution
Preface
For the newly joined iGEMers, understanding the current research status of the former iGEMers is the first homework. Based on the difficulties we encountered when searching for information and summarizing, we did the following summary and sorting work. At the same time, we also hope that this work can continue to provide a rich introductory database for future iGEMers, who is interested in the subject of plastic degradation. This is our original intention to arrange this contribution work. In the future, we strongly suggest that an open-access plastic degradation resource sharing platform should be constructed.
Polyethylene terephthalate (PET) is one of the most important synthetic polymers, at the same time, is also one of
the main pollutants in the environment. For a long time, the scientific community has been looking for effective
methods of PET biodegradation. In iGEM environment track, plastic pollution treatment is also one of the hottest
issues.
Since Japanese researchers discovered a magical bacterium (Ideonella sakaiensis 201-F6) that can "eat plastic"1,
encouraging advances related to the biodegradation of PET plastic appear frequently.
In order to save the time of searching and sorting information for the new iGEMers. we reviewed the related
projects over the years and summarized the successful projects results as follows (Table 1).
In summary, the previous iGEM teams are mainly committed to solving the problems related to PET degradation: 1)
improving the degradation efficiency and 2) improving the thermal stability of PETase (2019 Exeter). 3) Improving
the secretion efficiency of PETase if necessary (2018 Yale). Details are as follows (Table 1).
Table 1 Previous Projects of iGEM team on PET degradation
1. Improving the degradation efficiency
For improving the efficiency of enzyme degradation, TJUSLS China (2016) had two paths, one is directed mutation,
and the other is surface display, that helps in greatly improving the enzyme activity. Harvard BioDesign (2016)
found that T7 lysY Iq was the optimal strain to express PETase in. Exeter (2019) were aiming to identify the most
efficient combination of PETase and MHETase mutants. All of these team were successfully constructed the parts. In
particular, TU Kaiserslautern (2019) was the first iGEM team working with a eukaryotic organism, these data
indicate that spontaneous conversion when used BHET as substrate to MHET is enhanced 10-fold at 40°C versus 30°C.
In addition, researchers reported that X-ray crystallography has been successfully used to analyze the structure
of high-resolution PET hydrolase, high-efficient PETase mutants were constructed by protein engineering
technology[2-4]. In 2020, the researchers genetically engineered leaf branch compost cutinase to improve the
efficiency of plastic decomposition. This mutant enzyme is 10000 times more efficient in cutting PET chemical
bonds than natural enzymes. They found that the mutant enzyme they produced was able to break down 200g of PET in
10 hours with 90% efficiency [5]. This highly efficient and optimized enzyme performs better than all the PET
hydrolases, including Ideonella sakaiensis strain 201-F6 and related modified variants[2,6-8]. Researchers are now
working to further improve the efficiency of enzyme, hoping to eventually be used in the degradation of industrial
plastics.
2. Improving thermal stability of PETase
Toronto (2019) was to further optimize the thermostability and catalytic ability of PETase. The catalytic activity of all their constructed variants was 6-fold higher than wild type. Sequence alignment of PETase and the thermostable PHEs might identify amino acids that could impart higher thermostability to PETase[9].
3. Improving the secretion efficiency of PETase if necessary
Yale (2018) engineered E. coli to express and secrete PETase and MHETase for extracellular degradation of PET, and aimed to tackle PET pollution by genetically engineering a synthetic Escherichia coli and Aceintobacter baylyi co-culture to degrade and metabolize PET. The catalytic activity they constructed was 1.5-fold higher than control.
4. Other possible references
Berlin (2015) used natural products produced by microorganisms to design the flagelluloseas a scaffold for
enzymes(microorganisms). And they were successfully constructed the parts. In 2019, the researchers reported PET
degradation by a microbial consortium and its bacterial resident, Ideonella sakaiensis[9].
Although there were still several problems to be solved, more applications involving PET hydrolase can be
foreseen. Further understanding of the molecular mechanism of PET hydrolase will provide an ideal starting point
for the identification of related enzymes in the future. Therefore, we have a vision of an environmentally
friendly approach for recycling PET through synthetic biology.
References:
[1] Shosuke Yoshida. et al. A bacterium that degrades and assimilates poly (ethylene
terephthalate). Science. 2016;351(6278):1196-9.
[2] Xu Han. et al. Structural insight into catalytic mechanism of PET hydrolase. Nat
Commun. 2017;8(1):2106.
[3]Yuan Ma. et al. Enhanced Poly(ethylene terephthalate) Hydrolase Activity by Protein
Engineering. Engineering. 2018;888-893.
[4]Harry P. et al. Characterization and engineering of a plastic-degrading aromatic
polyesterase. PNAs. 2018; 115(19): E4350–E4357
[5]V Tournier. et al. An engineered PET depolymerase to break down and recycle plastic
bottles. Nature. 2020;580(7802):216-219.
[6]Joo S. et al. Structural insight into molecular mechanism of poly(ethylene terephthalate)
degradation. Nat Commun. 2018;9(1):382.
[7]Harry P Austin. et al. Characterization and engineering of a plastic-degrading aromatic
polyesterase. Proc Natl Acad Sci USA. 2018;115(19):E4350-E4357.
[8]Taniguchi I. et al. Biodegradation of PET: current status and application aspects. ACS
Catal. 2019;9:4089–4105.
[9]Ikuo Taniguchi. et al. Biodegradation of PET: Current Status and Application Aspects.
ACS Catal. 2019;9:4089−4105