摘要：

The CooA family of proteins are prokaryotic CO-sensing transcription factors that regulate the expression of genes involved in the utilization of CO as an energy source. These are homo-dimeric proteins that contain two heroes. Each monomer contains an N-terminal heme-binding domain and a C-terminal DNA-binding domain. Binding of CO to the heme leads to activation by a large reorientation of the DNA-binding domain such that the DNA-binding domain is in position for specific DNA recognition. The crystal structure of CooA from Rhodospirillum rubrum (RrCooA) (Lanzilotta et al., 2000) in the inactive CO-free off-state shows that the N-terminal Pro residue of monomer A coordinates the heme of monomer B and vice versa. It now appears that the CO replaces the Pro ligand and that this change is coupled to the activation process. However, precisely how replacement of the Pro ligand by CO results in structural changes some 25Å from the CO binding site remains unknown. Here we report the structure of a CooA variant from thermophilic bacterium Carboxydothermus hydrogenoformans (ChCooA) where one monomer is in the fully on-state. The N-terminal region that is displaced by CO binding is now positioned between the heme- and DNA-binding domains which requires movement of the N-terminus by ∼20Å and thus serves as a bridge between the two domains that helps to orient the DNA-binding domain in position for DNA binding.

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