Composite Part 1:

FucO/ L-1,2-Propanediol Oxidoreductase

FucO is the gene that codes for L-1,2-propanediol oxidoreductase which is a NADH-linked, homodimer enzyme having the role of acting on furfural which is a toxic inhibitor of microbial fermentations causing cell wall and membrane damage, DNA breaks down and reduced enzymatic activities (Zheng, 2013; Liu, Ma & Song, 2009).

The enzyme catalyzes L-lactaldehyde and L-1,2- propanediol while dissimilating fucose in which acetaldehyde, ethylene glycerol, L-lactaldehyde and some more substances are used as substrates. Despite these, it takes an important role in furan reduction to its alcohol derivative (Wang et al., 2011).

Our circuit design for FucO gene

Our circuit consists of prefix, a strong promoter (J23100), RBS (B0034), FucO as protein coding region, double terminator (B0015) and suffix. This part enables our E. coli KO11 strain to convert toxic furfural into furfuryl alcohol. Our construct is inserted into pSB1C3 and delivered to the Registry.

FucO has NADH-dependent furan reductase activity. When furfural is present in the field, the metabolism of furfural by NADPH-dependent oxidoreductases go active in order to reduce it to its less toxic alcohol derivative-furfuryl alcohol (Zheng, 2013; Wang et al., 2013; Allen et al., 2010).

In this metabolism, the expression of oxidoreductases that are NADPH-dependent, such as YqhD, are shown to inhibit the growth and fermentation in E. coli by competing for biosynthesis with NADPH (Zheng, 2013).

Because the native conversion of NADH to NADPH in E. coli is insufficient to revitalize the NADPH pool during fermentation, the actions shouldn’t be interfering with NADPH metabolism (Wang et al., 2011). Thus, the overexpression of plasmid-based NADH-dependent propanediol oxidoreductase (FucO) gene may reduce furfural to ultimately improve furfural resistance without detrimentally affecting the biosynthesis of NADPH (Wang et al., 2011).

Figure 2: The overexpression of FucO and YqhD and relationships with furfural resistance traits, metabolism, and reducing cofactors (Wang et al., 2013).

In order to make our gene compatible with RFC 10, 25 and 1000, we reconstructed the nucleotides to get rid of the restriction sites while protecting the amino acid sequence. We looked through the codon bias property of E. coli and made the nucleotide changes accordingly.

We’ve inserted the FucO composite part to pSB1C3 and pSB1A3 backbones. Then, we’ve transformed the construct for submission, BBa_K2571003, (in pSB1C3) to Dh4 alpha; and the other construct, for our biochemical assay, (in pSB1A3) to KO11. As we isolated the plasmids, we’ve done PCR with FucO left and VR primers to test orientation of our parts to the backbone. We expected a band of 754 bp between the FucO left and VR primers and the PCR results confirmed our expectations and showed that our parts were correctly inserted and transformed.

Composite 2:

GSH:Bifunctional gamma-glutamate-cysteine ligase/glutathione synthetase

Glutathione (GSH) is an important antioxidant that has a sulfur compound; a tripeptide composed of three amino acids (cysteine, glycine and glutamic acid) and a non-protein thiol (Pizzorno, 2014; Lu, 2013). GSH is generally found in the thiol-reduced from which is crucial for detoxification of ROS and free radicals which cause oxidative stress (Lu, 2013; Burton & Jauniaux, 2011).

Reactive Oxygen Species are dangerous substances that distort protein based matters by taking electrons (Lu, 2013). The chemical structure of the protein-based substances are altered and become dysfunctional because of ROS (Lu, 2013; Burton & Jauniaux, 2011).

Furthermore, one of the most significant protein-based substance, DNA get attacked by OH radicals (Burton & Jauniaux, 2011). However, the reduced form GSH can protect the chemical structure of the proteins by giving extra electrons to the ROS and free radicals (Lu, 2013). This is accomplished by GSH peroxidase-catalyzed reactions (Lu, 2013).

In order to make our gene compatible with RFC 10, 25 and 1000, we reconstructed the nucleotides to get rid of the restriction sites while protecting the amino acid sequence. We looked through the codon bias property of E.coli and made the nucleotide changes accordingly.

Our circuit design for GSH gene

Our circuit consists of prefix, a strong promoter (J23100), RBS (B0034), GSH as A protein coding region, double terminator (B0015) and suffix. This part enables our E. coli KO11 strain to overexpress Oxidised Glutathione to reduce oxidative stress, increasing its lifespan. (Lu, 2013) Our construct is inserted into pSB1C3 and delivered to the Registry.

We’ve inserted the GSH composite part to pSB1C3 backbone. Then, we’ve transformed the construct for submission, BBa_K2571005, (in pSB1C3) to Dh4 alpha and conducted colony PCR. We’ve made the PCR with GSH specific primers and expected to see a result of 225bp. By showing the band we expected, 225bp, PCR confirmation for our insertion proved right.

Composite 3:

Dual Expression of FucO and GSH

The first protein coding region we have, placed after the RBS, FucO, will code for L-1,2-propanediol oxidoreductase (a homodimer enzyme) in order to act upon furfural presence in the field (Zheng, 2013). The metabolism of furfural by NAD(P)H-dependent oxidoreductases will reduce the toxicity of the chemical by turning it into furfuryl alcohol, a derivative and increase the furfural tolerance (Zheng, 2013; Wang et al., 2013; Allen et al., 2010). Our second protein coding region, bifunctional gamma-glutamate-cysteine ligase/glutathione synthetase (GSH), is a non-protein thiol group and a tripeptide composed of cysteine, glycine and glutamic acid (Lu, 2013). It is crucial for the detoxification of reactive oxygen species and free radicals (Ask et al, 2013). Reactive oxygen species (ROS) are harmful substances that alter protein based matters by taking electrons (Lu, 2013; Burton & Jauniaux, 2011). Because many benefits of GSH include scavenging of ROS, protection against endogenous toxic metabolites and detoxification of xenobiotics, we choose this gene to entagrate with the FucO (Höck et al., 2013). Thus we constructed multi functional gene providing long life span and resistance.

Design Notes of Dual Expression of FucO and GSH

Our construct for composite part 3 is composed of two stages, first the reduction of furans (specifically furfural and 5-HMF) and second the detoxification of reactive oxygen species (ROS). Our first composite part, fucO gene coding for L-1,2-propanediol oxidoreductase along with the promoter J23100, RBS B0034 and double terminator B0034, is NADH-dependent, which highly benefits to the construct of our project. Our construct is inserted into pSB1C3 and delivered to the Registry.

As fucO is NADH-dependent it outperforms other oxidoreductases, by not interfering with the NADPH metabolism of the organism while converting highly toxic substances, furfural and 5-HMF to non-harmful alcohols. This characteristic of fucO is crucial because the expression of oxidoreductases like Yqhd are NADPH-dependent, hence they compete with the biosynthesis for NADPH, which results in inhibiting the growth of the organism.