Many chemicals produced by plants, animals and other organisms in nature have become vital building blocks in the medicines we use to treat disease, but to produce these building blocks at a mass scale often requires the use of chemical catalysts that may be expensive and produce waste that is harmful to the environment. To produce more environmentally-friendly medicines and other products, scientists are turning back to nature and taking inspiration from the processes that plants use to biosynthesize these vital components. Researchers at the University of Warwick have now developed a method to produce indolic amides, carboxylic acids and auxins – key components in both pharmaceutical and agrochemical products – using engineered bacteria and enzymes that mimic the indole-3-acetamide (IAM) pathway of plants.
In order to reproduce the natural production methods of plants, the researchers worked to reconstruct the IAM pathway in E. coli cells. The team investigated plants and plant-associated bacterial species for genetic insights into the expression of two key enzymes – tryptophan-2-monooxygenase (iaaM) and indole-3-acetamide hydrolase (iaaH) – that play a role in the biosynthesis of valuable molecules such as indole-3-acetic acid (IAA) and its derivatives. With insights from the plant microbiome, the researchers were able to engineer E. coli to overexpress iaaM and iaaH such that the enzymes can be easily separated for reactions in mild and aqueous conditions, or used directly in the bacteria to facilitate reactions.
The benefits of this method include not only the bacteria’s ability to quickly reproduce and express these key enzymes, but also the ability to synthesize the desired products from inexpensive materials like glucose. With the addition of enzymes like tryptophan synthase (Trp_syn) or flavin-dependent halogenase (Fl-Hal) along with iaaM and iaaH, a scalable one-pot cascade reaction can be performed to yield IAA and its derivatives from low-cost indole or tryptophan without additional catalysts. In addition, encapsulating the natural catalysts in a cross-linked enzyme aggregate (CLEA) can improve the performance of the reactions and allow the catalysts to be reused multiple times, the researchers found. This study was published in ACS Catalysis.
“We are basically harnessing the power of nature to solve many problems in the chemical, pharmaceutical, agriculture and manufacturing industries via engineering microbes and enzymes. Synthetic Biology is essentially using biology for synthetic purposes, and here we have displayed how blending and mixing it with different enzymes can be used with many similar molecules,” said Binuraj Menon, who led the research. “In the near future, additional engineering and lab-based evolution of these enzymes will allow us to prepare bespoke molecules and targeted chemicals.”
The use of enzymes and their cascade reactions as opposed to other chemical catalysts allows important molecules for pharmaceutical, agrochemical and other industrial applications to be synthesized at a large scale with less toxic waste and also at a lower cost. Additional strategies such as CLEA-based approaches can further improve upon and increase the scalability and sustainability of these nature-inspired methods.
Photo: The auxins used in this process are the same that cause the formation of crown galls in certain plants. Credit: Unversity of Warwick