Carbon Monoxide. Toxic Gas and Fuel for Anaerobes and Aerobes: Carbon Monoxide Dehydrogenases

Abstract

Carbon monoxide (CO) pollutes the atmosphere and is toxic for respiring organisms including man. But CO is also an energy and carbon source for phylogenetically diverse microbes living under aerobic and anaerobic conditions. Use of CO as metabolic fuel for microbes relies on enzymes like carbon monoxide dehydrogenase (CODH) and acetyl-CoA synthase (ACS), which catalyze conversions resembling processes that eventually initiated the dawn of life.CODHs catalyze the (reversible) oxidation of CO with water to CO2 and come in two different flavors with unprecedented active site architectures. Aerobic bacteria employ a Cu- and Mo-containing CODH in which Cu activates CO and Mo activates water and takes up the two electrons generated in the reaction. Anaerobic bacteria and archaea use a Ni- and Fe-containing CODH, where Ni activates CO and Fe provides the nucleophilic water. Ni- and Fe-containing CODHs are frequently associated with ACS, where the CODH component reduces CO2 to CO and ACS condenses CO with a methyl group and CoA to acetyl-CoA.Our current state of knowledge on how the three enzymes catalyze these reactions will be summarized and the different strategies of CODHs to achieve the same task within different active site architectures compared.

CODH‐IV: A High‐Efficiency CO‐Scavenging CO Dehydrogenase with Resistance to O2

“…Thus,o ur observations support the idea that CODH-IV is aC Oscavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected.Anaerobic microorganisms,b oth bacteria and archaea, employ Ni-and Fe-containing carbon monoxide dehydrogenases (CODHs) to reversibly reduce CO 2 to CO. [1][2][3] Ni,Fe-CODHs are homodimeric enzymes containing aN i,Fe,Scluster,t ermed cluster C, at their active site.C luster Ci s a[NiFe 3 S 4 OH x ]-cluster, where aNi II ion is integrated into an Fe/S scaffold forming ad istorted NiFe 3 S 4 -heterocubane with an additional exo Fe II ion with water/hydroxide coordination. Thus,o ur observations support the idea that CODH-IV is aC Oscavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected.…”

The concept of photochemical enzyme models – State of the art

“…In nature this difficult task is achieved by metalloenzymes such as CO-dehydrogenases (CODHs), which are able to catalyze the reversible multielectron transfer interconversion between carbon dioxide and carbon monoxide according to eq. 10 [152][153][154].…”

AcsF Catalyzes the ATP-dependent Insertion of Nickel into the Ni,Ni-[4Fe4S] Cluster of Acetyl-CoA Synthase

“…ACS and CODH can be found as independent monofunctional enzymes in Carboxydothermus hydrogenoformans (15) but are typically found in other microorganisms as protein complexes: in acetogens ACS and CODH form a bifunctional (␣␤) 2 complex, whereas in methanogens they are part of a large (␣␤␥␦⑀) 8 multienzyme complex (11,13,15,16). CODHs catalyze the reversible reduction of CO 2 to CO at the C-cluster, in which a single nickel ion, embedded within a 3Fe-4S scaffold with an additional iron in exo, binds and activates CO and CO 2 for turnover (17)(18)(19).…”