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

Abstract

CO dehydrogenases (CODHs) catalyse the reversible conversion between CO and CO . Genomic analysis indicated that the metabolic functions of CODHs vary. The genome of Carboxydothermus hydrogenoformans encodes five CODHs (CODH-I-V), of which CODH-IV is found in a gene cluster near a peroxide-reducing enzyme. Our kinetic and crystallographic experiments reveal that CODH-IV differs from other CODHs in several characteristic properties: it has a very high affinity for CO, oxidizes CO at diffusion-limited rate over a wide range of temperatures, and is more tolerant to oxygen than CODH-II. Thus, our observations support the idea that CODH-IV is a CO scavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected.

The two CO-dehydrogenases of Thermococcus sp. AM4

“…In the case of CODH 1, the current even slowly increases further during the minute that follows the injection, reflecting an increase in activity, probably an activation by CO. After the plateau, the current decreases in a sigmoidal fashion, ending in a perfect mono-exponential decay. This is exactly as observed in the case of other CODHs [15,23]. CODHs are in general so active for CO oxidation that the electrode rotation cannot prevent depletion of CO in the vicinity of the electrode: therefore, mass-transport limitations have to be taken into account.…”

“…Recently, we suggested that a tight packing of residues at the backside of the [3Fe-4S]subcluster of the C cluster can contribute to O 2 -resistance in Ch CODH IV, whereas the loose packing is typical of highly O 2 -sensitive CODHs [15]. Residues M556, F322, I206, C304, K559 and S557 of CooS2 are in close contact to the backside of the C cluster ( figure 3B), resembling more the tightly shielded backside of Ch CODH IV than the loosely packed Ch CODH II.…”

“…We have previously shown that the injection of a dissolved gas into an open electrochemical cell results in a near-instant increase in concentration followed by a perfectly mono-exponential decrease over time [21,33] (panel A in figure 5). This makes it possible to probe the response to a large range of substrate concentration in a single experiment, allowing the determination of even very small values of K m [15]. Figure 5 shows the response in current over time of films of CODH 1 and 2 poised at a constant potential after the injection of an aliquot of CO-saturated buffer.…”

“…Under normal growth conditions, the insertion of Ni into the C clusters depends on the accessory ATPase CooC, but in some cases the lack of cooC can be alleviated by an excess of Ni in the growth medium [13][14][15]. Besides the two cooC copies found in each of the two CODH clusters, TAM4 contains a third cooC copy (which we rename cooC3) located in a different part of the genome (TAM4_1296).…”

Maturation of the [Ni–4Fe–4S] active site of carbon monoxide dehydrogenases

“…The heterologous production in E. coli of Ch CODH-II or -IV, for instance, leads to the formation of nickel-loaded, mature and active CODH [8, 46, 47]. It is important to note that in these studies E. coli is grown in the presence of high concentrations of nickel (more than 0.5 mM) to favor nickel insertion into CODH.…”