CooA

CooA is a heme-containing transcription factor that responds to the presence of carbon monoxide. This protein is a homolog of cAMP receptor protein and forms homodimers. It induces the expression of carbon monoxide dehydrogenase, which oxidizes CO to CO2. The most well studied CooA homolog comes from "Rhodospirillum rubrum", but the CooA homolog from "Carboxydothermus hydrogenoformans" has been studied as well. For the CooA from "Rhodospirillum rubrum", the ferric heme iron is bound to cysteine thiolate and the amine of an N-terminal proline, in addition to the N4 donor set of the porphyrinate, and the protein is inactive. In the ferrous state, an imidazole of histidine displaces the thiolate. The midpoint potential is -300 mV. In the presence of CO, the secondary amine ligand provided by proline is displaced from Fe. It is this CO-bound form that interacts with DNA.