Redox Properties and Coordination Structure of the Heme in the CO-sensing Transcriptional Activator CooA

Transcriptional Activation 0301 basic medicine Alanine Escherichia coli Proteins Iron Heme Ligands Spectrum Analysis, Raman Oxygen 03 medical and health sciences Bacterial Proteins Models, Chemical Electrochemistry Mutagenesis, Site-Directed Histidine Cysteine Fimbriae Proteins Oxidation-Reduction
DOI: 10.1074/jbc.m003972200 Publication Date: 2002-07-26T15:09:37Z
ABSTRACT
The CO-sensing transcriptional activator CooA contains a six-coordinate protoheme as a CO sensor. Cys(75) and His(77) are assigned to the fifth ligand of the ferric and ferrous hemes, respectively. In this study, we carried out alanine-scanning mutagenesis and EXAFS analyses to determine the coordination structure of the heme in CooA. Pro(2) is thought to be the sixth ligand of the ferric and ferrous hemes in CooA, which is consistent with the crystal structure of ferrous CooA (Lanzilotta, W. N., Schuller, D. J., Thorsteinsson, M. V., Kerby, R. L., Roberts, G. P., and Poulos, T. L. (2000) Nat. Struct. Biol. 7, 876-880). CooA exhibited anomalous redox chemistry, i.e. hysteresis was observed in electrochemical redox titrations in which the observed reduction and oxidation midpoint potentials were -320 mV and -260 mV, respectively. The redox-controlled ligand exchange of the heme between Cys(75) and His(77) is thought to cause the difference between the reduction and oxidation midpoint potentials.
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