CO sensing and regulation of gene expression by the transcriptional activator CooA

The transcriptional activator CooA from Rhodospirillum rubrum contains a si x-coordinate protoheme that acts as a CO sensor in vivo. CO is a physiologi cal effector of CooA and replaces one of the axial ligands of the ferrous h eme to form the GO-bound CooA that is active as the transcriptional activat or. Cys(75) or His(77) is coordinated to the ferric and ferrous hemes in Co oA, respectively. The redox-controlled ligand exchange between Cys(75) and His(77) proceeds during the change in the redox state of the heme. The redu ction and oxidation midpoint potentials of CooA have been determined to be -320 and -260 mV, respectively. The properties of a functional chimera deri ved from CRP and CooA suggest that CooA activates the transcription by a si milar mechanism to that for CRP at Class II CRP-dependent promoters. Alanin e-scanning mutagenesis has revealed that Arg(24) and Arg(53) of CooA, which will be concerned with the protein-protein interaction with RNA polymerase , are critical amino acid residues for the transcriptional activator activi ty of CooA, and that Lys(26) and Asp(94) modulate the activity of CooA. (C) 2000 Elsevier Science BN. All rights reserved.