Structure and function of CooA, a novel transcriptional regulator containing a b-type heme as a CO sensor

CooA is a transcriptional activator containing a b-type heme as a prosthetic group. The heme in CooA is in the six-coordinate form in the ferric and ferrous state. Although the ferrous heme is coordinated by two axial ligands, it can react easily with CO to form the CO-bound heme under physiological conditions. Replacement of the heme's axial ligand by CO triggers the activation of CooA, which causes some conformational change around the heme and finally in the whole molecule. In this paper, the coordination structure of the heme in CooA and the mechanism of activation of CooA by CO were studied by spectroscopic analysis of the wild-type and some mutant CooAs. The amino acid residues responsible for the specific binding of CooA to target DNA were elucidated by site-directed mutagenesis. (C) 1999 Elsevier Science S.A. All rights reserved.