Diatomic Ligand Discrimination by the Heme Oxygenases from Neisseria meningitidis and Pseudomonas aeruginosa*
- ‡Departments of Molecular Biology and Biochemistry, of Physiology and Biophysics, and of Chemistry and the Center for Chemical and Structural Biology, University of California, Irvine, California 92697 and §Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201
- 1 To whom correspondence should be addressed. Tel.: 949-824-7020; Fax: 949-824-3280; E-mail: poulos{at}uci.edu.
Abstract
Heme oxygenases have an increased binding affinity for O2 relative to CO. Such discrimination is critical to the function of HO enzymes because one of the main products of heme catabolism is CO. Kinetic studies of mammalian and bacterial HO proteins reveal a significant decrease in the dissociation rate of O2 relative to other heme proteins such as myoglobin. Here we report the kinetic rate constants for the binding of O2 and CO by the heme oxygenases from Neisseria meningitidis (nmHO) and Pseudomonas aeruginosa (paHO). A combination of stopped-flow kinetic and laser flash photolysis experiments reveal that nmHO and paHO both maintain a similar degree of ligand discrimination as mammalian HO-1 and the HO from Corynebacterium diphtheriae. However, in addition to the observed decrease in dissociation rate for O2 by both nmHO and paHO, kinetic analyses show an increase in dissociation rate for CO by these two enzymes. The crystal structures of nmHO and paHO both contain significant differences from the mammalian HO-1 and bacterial C. diphtheriae HO structures, which suggests a structural basis for ligand discrimination in nmHO and paHO.
Footnotes
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↵2 The abbreviations used are: HO-1, mammalian heme oxygenase isozyme-1; nmHO, N. meningitidis heme oxygenase; paHO, P. aeruginosa heme oxygenase; cdHO, C. diphtheriae heme oxygenase; CO, carbon monoxide; NO, nitric oxide; O2, dioxygen; Heme, Fe-protoporphyrin IX; TCP, twin-coronet porphyrin; MD, molecular dynamics.
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↵* 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.
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- Received September 26, 2006.
- Revision received November 1, 2006.
- The American Society for Biochemistry and Molecular Biology, Inc.
