By Jenny Tang
Metabolic engineering can be best defined as manipulating a combination of genetic and regulatory processes within cells to increase production of a product. Although chemical synthesis was originally widely used to synthesize new pharmaceuticals, natural products have evolved for purposes other than human therapeutics. Using metabolic engineering, scientists can accelerate the production of chemicals, fuels, medicine, and pharmaceuticals. Some ways in which this is done is through the introduction of new genes whilst also balancing them to create a bottleneck in heterologous metabolic systems. These all involve careful experimentation before implementation into the human body. With the ever-growing knowledge of heterologous hosts such as Escherichia coli and Saccharomyces cerevisiae expanding, metabolism engineers can biosynthetically manipulate the expression of pathways and genes easier. These conserved mechanisms can be exploited to provide an insight to their biosynthetic application.[1]
Current pharmaceuticals from metabolic engineering
Creating medicine through metabolic engineering involves establishing or editing new metabolic pathways to ensure enhanced product formation. When desired characteristics are identified in one particular organism, such as a high diversity of the desired metabolite, it may need to be later transferred into a more ideal host for production. The most famous example of this is the drug insulin which requires the use of recombinant Escherichia coli. Transformation is another example of this using plant agrobacterium-mediated genetic transformation. This technique involves using the bacterial pathogen Agrobacterium tumefaciens to deliver genes of interest into a host plant. Some of the common drugs that have been produced from this method include Lipitor which is used to lower cholesterol.[1]
Isoprenoids
Metabolic manipulation to engineer pharmaceutical terpenoids has been heavily studied, as they belong in one of the most diverse and largest class of natural products. They have different curative effects on a wide range of diseases such as malaria, cancer, and cardiovascular diseases. Isoprenoids, a type of terpenoid, are synthesized from isoprenyl diphosphate units which are generated through the mevalonate pathway and the methylerythritol 4-phosphate (MEP) pathway. Synthesis occurs either through the Isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) precursors derived from either the MEP or mevalonate pathway. However, the main issue which this method is a precursor shortage. Two solutions are utilised: including overcoming rate-limiting enzymes or introducing alternative metabolic pathways for precursor synthesis.[2]
Diversification of pharmaceutical Polyketides
Pharmaceuticals derived from polyketides have anticancer, anticholeretic, antibiotic, and immunomodulator properties, displaying a large importance in medicine. Polyketides are synthesized through polyketide synthases and can be synthesized through a system called the plug and play, which is a type of technology that can automate chemical synthesis of each singular unit. Currently, polyketide biosynthetic pathways are exploited using organisms within the especially diverse Actinobacteria phylum. As gene clusters are in large numbers, thus creating a difficulty in engineering, alternative heterologous hosts are preferentially used, like Escherichia coli. [3]
Type I polyketide synthases have a multimodular functional organisation, and assembly-line styled architecture, both of which are ideal characterisations for metabolic engineering. Through the use of genetic analysis, the assembly line-styled architecture of the Type I polyketide synthases allows for accurate prediction of the formation of chemical productions through collinearity. Through using the modularity of the polyketide synthases, diversification of polyketide structures is progressing quickly. Modifications made to polyketide scaffolds can diversify the functionality of pharmaceuticals and as a result they have been developed into pharmaceuticals such as the commonly used immunosuppressant rapamycin.[3]
Production of L-valine through C. glutamicum
E.coli is used to produce L-valine which is a commonly used drug precursor but is also commonly used in muscle metabolism and to repair muscle tissue. It is one of the nine amino acids that higher organisms cannot synthesize and must be supplied through diet, hence it is most used as a nutritional supplement. Recent research has focused on increasing L-valine biosynthesis in the host Corynebacterium glutamicum.[4] The combination of transcriptomics and proteomics was critical to understanding the biosynthesis of L-valine production in C.glutamicum, which resulted in developing an industrial strain of VWB-1. Through inspection at a transcriptional level, 1155 differential genes expressed in ATTC 13869 (wildtype) and VWB-1 were identified. Genes that were heavily involved in the biosynthesis of L-valine, include ilvBN, ilvC, ilvD, ilvE, in the industrial strain which made significant contributions to increasing carbon flow towards L-valine. The NADPH and ATP generation ability was increased with the additional upregulation of genes involved within the phosphate pentose pathway and TCA pathway.[5]
Metabolic engineering in the field of synthetic biology is heavily used in commercialised medicine. Some widespread objectives include increasing production or diversifying the functionality of the product. Through this we can achieve exponentiation of the production of medication whilst also reducing the cost, especially. In 2017/2018, synthetic biology has dominated the list of the best-selling pharmaceuticals. Synthetic biology with the use of metabolic engineering currently dominates the pharmaceutical world and will allow for us to develop more revolutionary drugs.
References
1. Khosla C, Keasling JD. Metabolic engineering for drug discovery and development. Nature Reviews Drug Discovery. 2003 Dec;2(12):1019–25. Doi: 10.1038/nrd1256
2. Zu Y, Prather KL, Stephanopoulos G. Metabolic engineering strategies to overcome precursor limitations in isoprenoid biosynthesis. Current Opinion in Biotechnology. 2020 Dec;66:171–8. Doi: 10.1016/j.copbio.2020.07.005
3. Kornfuehrer T, Eustáquio AS. Diversification of polyketide structures via synthase engineering. MedChemComm [Internet]. 2019 May 10 [cited 2022 Oct 20];10(8):1256–72. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7053703/
4. Wang X, Zhang H, Quinn PJ. Production of l-valine from metabolically engineered Corynebacterium glutamicum. Applied Microbiology and Biotechnology. 2018 Mar 29;102(10):4319–30. Doi: 0.1007/s00253-018-8952-2
5. Zhang H, Li Y, Wang C, Wang X. Understanding the high l-valine production in Corynebacterium glutamicum VWB-1 using transcriptomics and proteomics. Scientific Reports [Internet]. 2018 Feb 26 [cited 2021 Sep 29];8(1):3632. Available from: https://www.nature.com/articles/s41598-018-21926-5
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