Heme oxygenases (HOs) oxidize heme to biliverdin, iron, and carbon monoxide (CO) via a complex, three-stage process that requires seven electrons and three molecules of O2. Interest in the heme oxygenases and their mechanisms has grown exponentially over the past few years as persuasive evidence has accumulated that these enzymes and their products, particularly CO and biliverdin, are physiologically important and clinically significant. CO functions as a messenger akin to nitric oxide, in part through activation of guanylyl cyclase, but also through action at other receptor and target sites. Furthermore, CO and biliverdin provide strong protection against inflammation, organ rejection in heart, kidney, and liver transplants, and neurological and cardiovascular disorders. HO itself has become a target of potential anticancer therapeutics due to its demonstrated antiapoptotic role. In previous work, we have used crystallography and NMR to elucidate the structure and mechanism of HO-1, one of the two active forms of the enzyme in humans. These studies have provided a cinematographic view of the conformations of the enzyme as it proceeds through the three-step oxidative process. In contrast, relatively little is known definitively about the structure and mechanism of HO-2, the second, constitutive form of human heme oxygenase. This enzyme differs from HO-1 in that it is a longer polypeptide and incorporates three heme regulatory motifs (HRMs), each of which has one cysteine residue. HO-1 has no cysteines. HO-2 has been specifically shown to be involved in the regulation of a potassium channel and control of a circadian rhythm clock. We now propose to elucidate the structural and mechanistic features of HO-2 that distinguish it from HO-1 and that enable it to fulfill unique biological functions. The following are the specific aims of the project: 1. Use studies of structure, mechanism, and dynamics to investigate the putative roles of the HRM domains of HO-2 as heme sinks, NO sinks, or as a redox sensor. 2. Elucidate the structural and conformational dynamics of human HO-2, with a focus on the carboxy terminal region in which the cysteine-containing heme regulatory motifs (HRMs) are located. 3. Define the differences in the catalytic mechanisms of HO-1 and HO-2, and clarify the overall mechanism of the latter steps of HO catalysis. 4. Define the interactions of HO-1 and HO-2 with naturally occurring polymorphic cytochrome P450 reductase (CPR) variants associated with human disease.

Public Health Relevance

Heme oxygenases degrade the heme group of hemoglobin and other hemoproteins to free iron, carbon monoxide, and biliverdin, which is, in turn, converted to bilirubin. The past decade has shown that the human heme oxygenases and the products they generate play critical roles as antioxidants, signaling molecules, and in maintenance of the body's iron supply. As a result the heme oxygenases suppress inflammation, help to prevent tissue rejection in transplants, are antiatherosclerotic, and play other important roles. At the same time, their antiapoptotic activity makes them targets for the design of inhibitors of potential utility in anticancer therapy.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK030297-30
Application #
8292238
Study Section
Macromolecular Structure and Function E Study Section (MSFE)
Program Officer
Bishop, Terry Rogers
Project Start
1982-01-01
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
30
Fiscal Year
2012
Total Cost
$253,905
Indirect Cost
$89,565
Name
University of California San Francisco
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94143
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Meitzler, Jennifer L; Ortiz de Montellano, Paul R (2011) Structural stability and heme binding potential of the truncated human dual oxidase 2 (DUOX2) peroxidase domain. Arch Biochem Biophys 512:197-203
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Evans, John P; Kandel, Sylvie; Ortiz de Montellano, Paul R (2009) Isocyanides inhibit human heme oxygenases at the verdoheme stage. Biochemistry 48:8920-8
Evans, John P; Niemevz, Fernando; Buldain, Graciela et al. (2008) Isoporphyrin intermediate in heme oxygenase catalysis. Oxidation of alpha-meso-phenylheme. J Biol Chem 283:19530-9
Ogura, Hiroshi; Evans, John P; de Montellano, Paul R Ortiz et al. (2008) Implication for using heme methyl hyperfine shifts as indicators of heme seating as related to stereoselectivity in the catabolism of heme by heme oxygenase: in-plane heme versus axial his rotation. Biochemistry 47:421-30
Jiang, Yongying; Ortiz de Montellano, Paul R (2008) Selenolate complexes of CYP101 and the heme-bound hHO-1/H25A proximal cavity mutant. Inorg Chem 47:3480-2

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