CooA is a
heme
Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...
-containing
transcription factor
In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...
that responds to the presence of
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
. This protein forms homodimers and is a homolog of
cAMP receptor protein. CooA regulates the expression of
carbon monoxide dehydrogenase, an enzyme that catalyzes the oxidation of CO to CO
2. The most well-studied CooA homolog comes from ''
Rhodospirillum rubrum
''Rhodospirillum rubrum'' (''R. rubrum'') is a Gram-negative, pink-coloured bacterium, with a size of 0.8-1 μm. It is a facultative anaerobe with a large set of possible metabolisms depending on the conditions of its environment. It's capable ...
'' (''RrCooA),'' but the CooA homolog from ''
Carboxydothermus hydrogenoformans'' (''Ch''CooA) has been studied as well. The main difference between these two CooA homologs is the ferric heme coordination. For ''Rr''CooA, the ferric heme iron is bound to a cysteine and the amine of the N-terminal proline, while, in the ferrous state, a ligand switch occurs where a nearby histidine displaces the thiolate. For ''Ch''CooA, the heme iron is ligated by a histidine and the N-terminal amine in both the ferric and ferrous states. For both homologs, CO displaces the amine ligand and activates the protein to bind to its target DNA sequence. Several structures of CooA exist: RrCooA in the ferrous state (1FT9), ChCooA in the ferrous, imidazole-bound state (2FMY), and ChCooA in the ferrous, CO-bound state (2HKX).
References
{{DEFAULTSORT:Transcription Factor
Gene expression
Protein families
DNA
Gaseous signaling molecules