The two CO-dehydrogenases of Thermococcus sp. AM4

Ni-containing CO-dehydrogenases (CODHs) allow some microorganisms to couple ATP synthesis to CO oxidation, or to use either CO or CO₂ as a source of carbon. The recent detailed characterizations of some of them have evidenced a great diversity in terms of catalytic properties and resistance to O₂. In an effort to increase the number of available CODHs, we have heterologously produced in Desulfovibrio fructosovorans, purified and characterized the two CooS-type CODHs (CooS1 and CooS2) from the hyperthermophilic archaeon Thermococcus sp. AM4 (Tc). We have also crystallized CooS2, which is coupled in vivo to a hydrogenase. CooS1 and CooS2 are homodimers, and harbour five metalloclusters: two [Ni4Fe-4S] C clusters, two [4Fe-4S] B clusters and one interfacial [4Fe-4S] D cluster. We show that both are dependent on a maturase, CooC1 or CooC2, which is interchangeable. The homologous protein CooC3 does not allow Ni insertion in either CooS. The two CODHs from Tc have similar properties: they can both oxidize and produce CO. The Michaelis constants (K_m) are in the microM range for CO and in the mM range (CODH 1) or above (CODH 2) for CO₂. Product inhibition is observed only for CO₂ reduction, consistent with CO₂ binding being much weaker than CO binding. The two enzymes are rather O₂ sensitive (similarly to CODH II from Carboxydothermus hydrogenoformans), and react more slowly with O₂ than any other CODH for which these data are available.