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J. Biol. Chem., Vol. 280, Issue 5, 3269-3274, February 4, 2005
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From the
Department of Structural Molecule Science, The Graduate University for Advanced Studies, 38 Nishigo-naka, Myodaiji, Okazaki 444-8585, the Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki 444-8787, and the ¶School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan
CooA is a CO-sensing transcriptional activator that contains a b-type heme as the active site for sensing its physiological effector, CO. In this study, the spectroscopic and redox properties of a new CooA homologue from Carboxydothermus hydrogenoformans (Ch-CooA) were studied. Spectroscopic and mutagenesis studies revealed that His-82 and the N-terminal 
-amino group were the axial ligands of the Fe(III) and Fe(II) hemes in Ch-CooA and that the N-terminal -amino group was replaced by CO upon CO binding. Two neutral ligands, His-82 and the N-terminal -amino group, are coordinated to the Fe(III) heme in Ch-CooA, whereas two negatively charged ligands, a thiolate from Cys-75 and the nitrogen atom of the N-terminal Pro, are the axial ligands of the Fe(III) heme in Rr-CooA. The difference in the coordination structure of the Fe(III) heme resulted in a large positive shift of redox potentials of Ch-CooA compared with Rr-CooA. Comparing the properties of Ch-CooA and Rr-CooA demonstrates that the essential elements for CooA function will be: (i) the heme is six-coordinate in the Fe(III), Fe(II), and Fe(II)–CO forms; (ii) the N-terminal is coordinated to the heme as an axial ligand, and (iii) CO replaces the N-terminal bound to the heme upon CO binding.
Received for publication, August 27, 2004 , and in revised form, November 2, 2004.
* This work was supported by a Grant-in-aid for Scientific Research of Priority Areas on Metal Sensors (12147203) from the Ministry of Education, Culture, Sports, Science, and Technology in Japan and by a Grant-in-Aid for Scientific Research B (16370065) from the Japan Society for the Promotion of Science. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
|| Present address: Dept. of Chemistry, Nagoya University, Furo, Chikusa, Nagoya 454-8602, Japan.
** To whom correspondence should be addressed. Tel.: 81-564-59-5575; Fax: 81-564-59-5576; E-mail: aono{at}ims.ac.jp.
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  M. Kubo, S. Inagaki, S. Yoshioka, T. Uchida, Y. Mizutani, S. Aono, and T. Kitagawa Evidence for Displacements of the C-helix by CO Ligation and DNA Binding to CooA Revealed by UV Resonance Raman Spectroscopy J. Biol. Chem., April 21, 2006; 281(16): 11271 - 11278. [Abstract] [Full Text] [PDF]
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