A Heterodimeric Reduced-Ferredoxin-Dependent Methylenetetrahydrofolate Reductase from Syngas-Fermenting Clostridium ljungdahlii

Abstract

Syngas, a mixture of CO, CO 2 , and H 2 , is the main component of steel mill waste gas and also can be generated by the gasification of biomass and urban domestic waste. Its fermentation to biofuels and biocommodities has attracted attention due to the economic and environmental benefits of this process. Clostridium ljungdahlii is one of the superior acetogens used in the technology.

Biosynthesis of L‐5‐methyltetrahydrofolate by genetically engineered Escherichia coli

“…The flavoprotein MTHFR can catalyse irreversibly the reduction of methylene‐THF to methyl‐THF using NADH as the source of reducing equivalents (Trimmer et al, 2001 ). MTHFR from E. coli is a homotetramer composed only of the MetF subunit, whereas MTHFR from C. autoethanogenum is an anaerobic enzyme composed of MetF and MetV subunits (Bertsch et al, 2015 ) that may use reduced 2[4Fe4S]‐ferredoxin as the reducing equivalent (Oppinger et al, 2021 ; Yi et al, 2021 ). DHFR from E. coli catalyses the reduction of folic acid to dihydrofolate and then reduces dihydrofolate to tetrahydrofolate using NADPH (Iwakura et al, 2006 ).…”

A Cytoplasmic NAD(P)H-Dependent Polysulfide Reductase with Thiosulfate Reductase Activity from the Hyperthermophilic Bacterium Thermotoga maritima

“…When indicated, 100 μM CoA was added to the mixture. For ferredoxin-related activity, a reduced ferredoxin regeneration system was added to the mixture instead of NAD(P)H. The reduced ferredoxin regeneration system contained 30 μM ferredoxin, 10 U Clostridium pasteurianum hydrogenase (CpI), and 100% gas-phase H 2 ( 40 ). To measure the formation of H 2 S, a modified double-vial technique ( 14 ) was used.…”

COx Fixation to Elementary Building Blocks: Anaerobic Syngas Fermentation vs. Chemical Catalysis

“…The ATP gain per one mole of acetate synthesized depends on the nature of the reducing equivalents (2[H]) used in those three reducing reactions in the methyl branch of the WLP. For M. thermoacetica this results in the formation of 0.5 ATP [82], whereas for C. ljungdahlii from -0.14 [123] www up to 0.63 [82] ATP per mole acetate have been proposed. CO can also be used directly in the carbonyl branch and saves one Fd red leading to higher ATP yield [124].…”

“…For M. thermoacetica this results in the formation of 0.5 ATP 82, whereas for C . ljungdahlii from –0.14 123 up to 0.63 82 ATP per mole acetate have been proposed. CO can also be used directly in the carbonyl branch and saves one Fd red leading to higher ATP yield 124.…”