Enzymology of the wood-Ljungdahl pathway of acetogenesis

Abstract

The biochemistry of acetogenesis is reviewed. The microbes that catalyze the reactions that are central to acetogenesis are described and the focus is on the enzymology of the process. These microbes play a key role in the global carbon cycle, producing over 10 trillion kilograms of acetic acid annually. Acetogens have the ability to anaerobically convert carbon dioxide and CO into acetyl-CoA by the Wood-Ljungdahl pathway, which is linked to energy conservation. They also can convert the six carbons of glucose stoichiometrically into 3 mol of acetate using this pathway. Acetogens and other anaerobic microbes (e.g., sulfate reducers and methanogens) use the Wood-Ljungdahl pathway for cell carbon synthesis. Important enzymes in this pathway that are covered in this review are pyruvate ferredoxin oxidoreductase, CO dehydrogenase/acetyl-CoA synthase, a corrinoid iron-sulfur protein, a methyltransferase, and the enzymes involved in the conversion of carbon dioxide to methyl-tetrahydrofolate.

FIGURE 1

The Wood–Ljungdahl pathway with the Eastern and Western branches depicted in red and blue, respectively. (In color in Annals on line.)

FIGURE 2

PFOR state including the HE-TPP radical, with the structure based on spectroscopic results, showing highly delocalized spin distribution (From Astashkin et al. Used with permission.), and the distance from HE-TPP radical to coupled cluster. Location of the clusters is based on the structure (PDB 1KEK).

FIGURE 3

ACS mechanism emphasizing the organometallic nature of the reaction sequence and the channel to deliver CO from the CODH active site to the A-cluster.

FIGURE 4

Random mechanism of acetyl-CoA synthesis.

FIGURE 5

Proposed conformers and interactions of the CFeSP. (Modified from Svetlitchnaia et al.79)