Skip to main content

Table 1 Estimated change in Gibbs energy and experimental validation for the reactions constituting the 2-oxoglutarate pathway

From: Discovery and implementation of a novel pathway for n-butanol production via 2-oxoglutarate

Step Reaction ΔrGm (KJ mol−1) Keq E.C. number Enzyme Gene NCBI accession no Enzymatic activitya Exp. validation in E. coli
1 2-Oxoglutarate + NADH + H+ 2-Hydroxyglutarateb + NAD+ − 22.6 ± 3.6 9.2 × 103 EC 1.1.1.399 2-Oxoglutarate reductase hgdH [AF]
WP_012938338
[19] [20, 21]
2 Acetyl-CoA + 2-Hydroxyglutarate Acetate + 2-Hydroxyglutaryl-CoA − 8.6 ± 15.3 32.1 EC 2.8.3.12 Glutaconate CoA-transferase (subunits α and β) gctA [AF]
WP_012939156.1
[22]
gctB [AF]
WP_012939155.1
3 2-Hydroxyglutaryl-CoA  Glutaconyl-CoA + H2O 0.7 ± 2.9 0.751 EC 4.2.1.167 (R)-2-Hydroxyglutaryl-CoA dehydratase
Subunits α, β and activator
hgdA [CS]
WP_003501726.1
[23]
hgdB [CS]
WP_003501727.1
hgdC [AF]
WP_012939153.1
[24]
4 Glutaconyl-CoA Crotonyl-CoA + CO2 − 35.8 ± 17.4 1.9 × 103 EC 1.3.8.6 Glutaryl-CoA dehydrogenase gcdH [PA]
WP_042912665.1
[25]
EC 4.1.1.70 Glutaconyl-CoA decarboxylase α subunit gcdA [CS]
WP_003501720.1
[26]
5 Crotonyl-CoA + NADH + H+ Butanoyl-CoA + NAD+ − 40.0 ± 17.0 1.0 × 107 EC 1.3.1.44 Trans-2-enoyl-CoA reductase ter [TD]
WP_002681770.1
[27] [5, 28,29,30]
6 Butanoyl-CoA + NADH + H+ Butanal + CoA + NAD+ − 57.0 ± 16 9.6 × 109 EC 1.2.1.57 Aldehyde/alcohol dehydrogenase adhE1 [CA]
WP_077851567.1
[31] [32, 33]
7 Butanal + NADH + H+ Butanol + NAD+ − 24.2 ± 4.8 1.8 × 104 EC 1.1.1.1
  1. The estimated change in Gibbs free energy (ΔrGm) values were computed with eQuilibrator [17] for each reaction constituting the novel pathway to produce butanol from 2-oxoglutarate (assumptions: reactant/product concentrations of 1 mM), as well as equilibrium constant (Keq) values at a pH of 7 and an ionic strength of 0.1 M. The encoding gene and respective microorganism, as well as references of enzymatic activity validation with the substrate and experimental validation in Escherichia coli are also shown, plus the EC number and NCBI accession number
  2. Exp experimental, EC enzyme commission, AF Acidaminococcus fermentans, CS Clostridium symbiosum, PA Pseudomonas aeruginosa, TD Treponema denticola, CA Clostridium acetobutylicum
  3. aThis refers to the substrate in italics in the reaction column
  4. bOnly the enzymes converting the (R)-isomer were considered. There are two enantiomers of 2-hydroxyglutarate; however, in KEGG (the database from which the reactions were retrieved), these variations are not represented. Depending on the enzyme, one of these forms can be preferably synthesized. The two subsequent reactions are part of the glutamate degradation pathway, existent is some microorganisms, where the (R)-isomers of the other compounds are preferably consumed