Researchers at the Korea Institute of Science and Technology have developed a novel method to produce unprecedentedly high levels of lutein through the use of systems metabolic engineering.
What is lutein and what makes it important enough to be worth the effort to produce it by genetically modifying bacteria? It is a xanthophyll—a class of natural carotenoid pigments that provide the rich, red, oranges, and yellows in fruits, vegetables, and even birds like flamingos. In addition to its contribution to the vibrant colours of flora and fauna, it is also present in the human eye, in the macula and retina, to safeguard the eye from oxidative damage by radiation. This helps lower the risk of common eye diseases, like cataracts and macular degeneration.
Currently, the lutein source for commercial products is produced from marigold flower extracts. However, this process is lengthy, low-yield, and expensive. These limitations have resulted in the inability of the production of commercial-grade lutein to be scaled up, making it hard for consumer demands for lutein to be met.
To solve this problem, scientists at the Korea Advanced Institute of Science and Technology (KAIST), including Dr. Seon Young Park, Ph.D. Candidate Hyunmin Eun, and Distinguished Professor Sang Yup Lee from the Department of Chemical and Biomolecular Engineering, developed a method to produce lutein using genetically modified Escherichia coli bacteria. Their work was featured in Nature Catalysis on August 5, 2022.
The team successfully created bacteria that could produce lutein using an economical raw material, glycerol, with systems metabolic engineering—an integrated technology to modify the metabolism of a microbe. There was a focus on resolving the inefficiencies in the biosynthetic mechanisms for the conversion of glycerol to lutein in a single cell throughout the system metabolic engineering process for higher yields and improved process efficiency.
First, the researchers modified the bacteria to be able to carry out the entire lutein biosynthesis pathway by the insertion of genes that produce the enzymes that enable the chemical transformation of glycerol to lutein. When the biosynthetic pathway was verified to be producing lutein in trace amounts in the genetically modified bacteria, the researchers moved on to improving the efficiency and yield of the lutein production pathway.
The enzymes that were deemed insufficient at enhancing the efficacy of the overall biosynthetic pathway were identified, and further studies were conducted to find the root causes of their inefficiencies. It was found that a promiscuous enzyme that catalyses two or more different reactions in the pathway and electron-requiring cytochrome P450 enzymes were the two targets that had to have their efficiencies enhanced further in order to increase the efficiency of lutein biosynthesis.
To address the limitations of the promiscuous enzymes, a method called substrate channelling was used to artificially recruit enzymes closer to each other such that the intermediates produced by one enzyme may be more quickly move to the next enzyme, reducing the time required for the complete conversion of glycerol to lutein, while also minimising the formation of undesirable byproducts.
Similarly, to enhance the performance of the electron-requiring cytochrome P450 enzymes, electron channelling was utilised to boost the concentrations of electron substrates surrounding the enzymes, allowing for increased rates of redox reactions carried out by P450 and its partner enzymes, to streamline the metabolic flux and produce more lutein molecules per unit time, and together with substrate channelling, allowing the bacteria to produce unprecedentedly high levels of lutein. The electron channelling strategy was also found to increase the efficiency of production of other metabolites such as apigenin and nootkatone in E. coli, indicating that this method may have general uses in systems metabolic engineering.
“It is expected that this microbial cell factory-based production of lutein will be able to replace the current plant extraction-based process,” said Dr. Seon Young Park, the first author of the paper. She also noted that the integrated metabolic engineering techniques might be useful for the production of other biochemicals for pharmacological or nutritional uses.
“As maintaining good health in an ageing society is becoming increasingly important, we expect that the technology and strategies developed here will play pivotal roles in producing other valuable natural products of medical or nutritional importance,” explained Distinguished Professor Sang Yup Lee.
Source: Park et al. (2022). Metabolic engineering of Escherichia coli with electron channelling for the production of natural products. ;Nature Catalysis, 1-12.