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

• DOI: 10.1074/jbc.m003972200
• Publication Date: 2002-07-26T15:09:37Z
• Authors: Hiroshi Nakajima; Yumiko Honma; Toshifumi Tawara; Toshiyuki Kato; Sam-Yong Park; Hideyuki Miyatake; Yoshitsugu Shiro; Shigetoshi Aono
• Keywords: 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

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.