CODehydrogenase/Acetyl‐CoASynthase

Abstract

The bifunctional tetrameric (α 2 β 2 ) enzyme carbon monoxide dehydrogenase (CODH)/acetyl‐CoA synthase (ACS) is a central component of the Wood‐Ljungdahl pathway of acetogenic bacteria. In this pathway, two CO 2 molecules are reduced to a methyl group by folate‐containing enzymes and to CO by CODH, respectively. These two substrates are subsequently combined in ACS to form an Ni‐bound acetyl group that is reductively eliminated as acetyl‐CoA. The CODH and ACS active sites are about 70 Å apart and are connected by a network of hydrophobic tunnels. Thus, CO produced at the former enzyme migrates inside the bifunctional protein to the ACS site. Site‐directed mutagenesis has confirmed the functional role of the tunnels. The ACS subunit undergoes a conformational change that blocks the tunnel near the active site, preventing the escape of the toxic CO from within the enzyme upon methyl binding to nickel.

Novel Domain Arrangement in the Crystal Structure of a Truncated Acetyl-CoA Synthase from Moorella thermoacetica,

“…Ni-dependent acetyl-coenzyme A synthase (ACS) is a NiFeS-cluster enzyme that requires strict anoxic conditions to function. In the acetogenic bacterium Moorella thermoacetica ( Mot ), the ACS α-subunit forms an α 2 β 2 heterotetramer with the Ni-containing carbon monoxide dehydrogenase (CODH) β-subunit . This association constitutes the central enzyme complex of the anaerobic Wood−Ljungdahl pathway of acetyl-CoA synthesis from CO 2 , .…”