|
Project Topic
|
Microbes are routinely engineered to synthesise chemicals from renewable materials. Improvements in microbial engineering are accelerating the global transition to a sustainable bio-based economy, as more chemicals are made in a manner similar to beer brewing, rather than being refined from oil. At the heart of microbial synthesis are enzymes that catalyse the reactions that produce the chemicals. Harnessing enzymes can be straightforward: genes encoding enzymes that perform the needed chemistry are installed into a microbial species, which then produces the chemical. However, while cells readily manufacture enzymes from other species, often the enzymes cannot perform the needed chemistry. This prevents microbial engineers from using such enzymes, and as a result, many chemicals still cannot be made by microbes on a useful scale. This problem is severe for enzymes known as iron-sulfur (FeS) enzymes. These enzymes must obtain iron (in the form of FeS clusters) and electrons from their host cell, just like many devices need batteries and electricity. If we can better equip FeS enzymes with FeS clusters, we will improve their activity, making it possible to produce even more chemicals with microbes and further push the development of a bio-based economy. In cells, iron and electrons are supplied to FeS enzymes by proteins that act as distribution networks. If the FeS enzymes are abundant (i.e. when overexpressed as part of an engineered pathway), these networks lack the capacity to deliver FeS clusters and electrons to FeS enzymes, and the FeS enzymes function poorly. Even worse, FeS enzymes taken from foreign species cannot “plug in” to the cellular networks. Using FeS enzymes to make chemicals therefore requires either an upgrade in the distribution network capacity to better supply FeS clusters and electrons, or adapters that enable the enzymes to plug in to the cell’s grid (just like electrical devices need adapters when traveling abroad). We find that foreign FeS enzymes can be better activated if parts of the distribution network from the foreign species (A-type FeS carriers, or “plug adapters”) are also abundantly supplied. Inspired by our success, we will use improved FeS cluster and electron distribution networks to improve the activity of an FeS enzyme (IspG) that can be harnessed to make a family of compounds (isoprenoids), which includes biofuels, solvents, and fragrances. IspG is notorious for its poor activity, and research suggests this is due to an insufficient supply of FeS clusters and electrons. As a result, microbial engineers often rely upon a less-efficient isoprenoid synthesis pathway that avoids IspG entirely. Our Consortium has identified the A-type carriers that activate IspG enzymes with FeS clusters, and it is further known that supplying more electrons to IspG improves its function. We will improve the cellular distribution networks linked to IspG to help it produce isoprenoids more efficiently. We will then move our tests from the lab bench to an industrial setting by improving an efficient IspG-dependent fermentation process that manufactures fragrances and flavours from sustainable sources. We will also search genomes for plug adapters to activate additional types of FeS enzymes. Activating FeS enzymes beyond IspG will demonstrate how to activate unique FeS enzymes, such as those needed to produce novel antibiotics. Such an approach will vastly expand the chemical versatility of engineered microbes. Our Consortium will also design and evolve proteins that deliver FeS clusters to a broader range of FeS enzymes. Such proteins might act like universal power adapters, which could relieve the need to find a specific plug adapter for each FeS enzyme. We will also study how and why FeS enzymes and power grid components interact, or fail to interact. This will help us to better use FeS delivery systems, and further improve the performance of FeS enzymes.
|
