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The reductive acetyl-CoA pathway

The Wood–Ljungdahl pathway is a set of biochemical reactions used by some bacteria. It is also known as the reductive acetyl-coenzyme A ( acetyl-CoA) pathway. [1] This pathway enables these organisms to use hydrogen (H2) as an electron donor, and carbon dioxide (CO2) as an electron acceptor and as a building block for biosynthesis.

In this pathway carbon dioxide is reduced to carbon monoxide (CO) and formic acid (HCOOH) or directly into a formyl group (R−CH=O), the formyl group is reduced to a methyl group (−CH3) and then combined with the carbon monoxide and coenzyme A to produce acetyl-CoA. Two specific enzymes participate on the carbon monoxide side of the pathway: CO dehydrogenase and acetyl-CoA synthase. The former catalyzes the reduction of the CO2 and the latter combines the resulting CO with a methyl group to give acetyl-CoA. [1] [2]

Some anaerobic bacteria use the Wood–Ljungdahl pathway in reverse to break down acetate. For example, sulfate-reducing bacteria (SRB) transform acetate completely into CO2 and H2 coupled with the reduction of sulfate to sulfide. [3] When operating in the reverse direction, the acetyl-CoA synthase is sometimes called acetyl-CoA decarbonylase.

Not to be confused with the Wood-Ljungdahl pathway, an evolutionarily related but biochemically distinct pathway named the Wolfe Cycle [4] occurs exclusively in some methanogenic archaea called methanogens. [5] In these anaerobic archaea, the Wolfe Cycle functions as a methanogenesis pathway to reduce CO2 into methane (CH4) with electron donors such as hydrogen (H2) and formate (HCOO–). [6]

Evolution

Relevance to abiogenesis

Main article: Iron–sulfur world hypothesis

It has been proposed that the reductive acetyl-CoA pathway might have begun at deep sea alkaline hydrothermal vents where metal sulfides and transition metals catalyze the prebiotic reactions of the reductive acetyl-CoA pathway. [7] Recent experiments have tried to replicate this pathway by attempting to reduce CO2, with very little pyruvate observed using native iron (Fe0, zerovalent Fe) as a reducing agent (< 30 μM), [8] and even less so under hydrothermal settings with H2 (10 μM). [9] Joseph Moran and colleagues state that "it has been proposed that either the complete or “horseshoe” forms of the r TCA cycle may have once been united with the acetyl CoA pathway in an ancestral, possibly prebiotic, carbon fixation network". [8]

Last universal common ancestor

A 2016 study of the genomes of a set of bacteria and archaea suggested that the last universal common ancestor (LUCA) of all cells was using an ancient Wood–Ljungdahl pathway in a hydrothermal setting, [10] but more recent work challenges this conclusion as they argued that the previous study had "undersampled protein families, resulting in incomplete phylogenetic trees which do not reflect protein family evolution". [11] However geological evidence and phylogenomic reconstructions of the metabolic network of the common ancestors of archaea and bacteria support that LUCA fixed CO2 and relied on H2. [12] [9]

Historical references

  • Ljungdahl LG (1969). "Total synthesis of acetate from CO2 by heterotrophic bacteria". Annual Review of Microbiology. 23 (1): 515–38. doi: 10.1146/annurev.mi.23.100169.002503. PMID  4899080.
  • Ljungdahl LG (1986). "The autotrophic pathway of acetate synthesis in acetogenic bacteria". Annual Review of Microbiology. 40 (1): 415–50. doi: 10.1146/annurev.micro.40.1.415. PMID  3096193.
  • Ljungdahl LG (2009). "A life with acetogens, thermophiles, and cellulolytic anaerobes". Annual Review of Microbiology. 63 (1): 1–25. doi: 10.1146/annurev.micro.091208.073617. PMID  19575555.

See also

References

  1. ^ a b Ragsdale Stephen W (2006). "Metals and Their Scaffolds To Promote Difficult Enzymatic Reactions". Chem. Rev. 106 (8): 3317–3337. doi: 10.1021/cr0503153. PMID  16895330.
  2. ^ Paul A. Lindahl "Nickel-Carbon Bonds in Acetyl-Coenzyme A Synthases/Carbon Monoxide Dehydrogenases" Met. Ions Life Sci. 2009, volume 6, pp. 133–150. doi: 10.1039/9781847559159-00133
  3. ^ Spormann, Alfred M.; Thauer, Rudolf K. (1988). "Anaerobic acetate oxidation to CO2 by Desulfotomaculum acetoxidans". Archives of Microbiology. 150 (4): 374–380. doi: 10.1007/BF00408310. ISSN  0302-8933. S2CID  2158253.
  4. ^ Thauer, Rudolf K. (2012). "The Wolfe cycle comes full circle". Proceedings of the National Academy of Sciences of the United States of America. 109 (38): 15084–15085. doi: 10.1073/pnas.1213193109. PMC  3458314. PMID  22955879.
  5. ^ Matschiavelli, N.; Oelgeschlager, E.; Cocchiararo, B.; Finke, J.; Rother, M. (2012). "Function and regulation of isoforms of carbon monoxide dehydrogenase/acetyl-CoA synthase in Methanosarcina acetivorans". Journal of Bacteriology. 194 (19): 5377–87. doi: 10.1128/JB.00881-12. PMC  3457241. PMID  22865842.
  6. ^ Lyu, Z.; Shao, N.; Akinyemi, T.; Whitman, WB. (2018). "Methanogenesis". Current Biology. 28 (13): R727–R732. doi: 10.1016/j.cub.2018.05.021. PMID  29990451.{{ cite journal}}: CS1 maint: multiple names: authors list ( link)
  7. ^ Russell, M. J.; Martin, W. (2004). "The rocky roots of the acetyl-CoA pathway". Trends in Biochemical Sciences. 29 (7): 358–363. doi: 10.1016/j.tibs.2004.05.007. ISSN  0968-0004. PMID  15236743.
  8. ^ a b Varma, Sreejith J.; Muchowska, Kamila B.; Chatelain, Paul; Moran, Joseph (2018-04-23). "Native iron reduces CO2 to intermediates and end-products of the acetyl-CoA pathway". Nature Ecology & Evolution. 2 (6): 1019–1024. doi: 10.1038/s41559-018-0542-2. ISSN  2397-334X. PMC  5969571. PMID  29686234.
  9. ^ a b Preiner, Martina; Igarashi, Kensuke; Muchowska, Kamila B.; Yu, Mingquan; Varma, Sreejith J.; Kleinermanns, Karl; Nobu, Masaru K.; Kamagata, Yoichi; Tüysüz, Harun; Moran, Joseph; Martin, William F. (April 2020). "A hydrogen-dependent geochemical analogue of primordial carbon and energy metabolism" (PDF). Nature Ecology & Evolution. 4 (4): 534–542. doi: 10.1038/s41559-020-1125-6. ISSN  2397-334X. PMID  32123322. S2CID  211729738.
  10. ^ M. C. Weiss; et al. (2016). "The physiology and habitat of the last universal common ancestor". Nature Microbiology. 1 (16116): 16116. doi: 10.1038/nmicrobiol.2016.116. PMID  27562259. S2CID  2997255.
  11. ^ S. J. Berkemer; et al. (2021). "A new analysis of archaea-bacteria domain separation: Variable phylogenetic distance and the tempo of early evolution". Molecular Biology and Evolution. 37 (8): 2332–2340. doi: 10.1093/molbev/msaa089. PMC  7403611. PMID  32316034.
  12. ^ Xavier, Joana C.; Gerhards, Rebecca E.; Wimmer, Jessica L. E.; Brueckner, Julia; Tria, Fernando D. K.; Martin, William F. (2021-03-26). "The metabolic network of the last bacterial common ancestor". Communications Biology. 4 (1): 413. doi: 10.1038/s42003-021-01918-4. ISSN  2399-3642. PMC  7997952. PMID  33772086.

Further reading

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