Cytochrome c peroxidase (CcP) is a detoxification enzyme, designed to maintain low levels of intracellular H2O2 levels by reducing the H2O2 to water. The catalytic mechanism couples the two- electron reduction of H2O2 to two single-electron-transfer steps involving ferrocytochrome c. CcP initially reduces H2O2 to water generating an enzyme intermediate called CcP compound I (CcP-I). CcP-I is oxidized two equivalents above the native FeIII state of the CcP with the two oxidized sites identified as an FeIV heme and an oxidized tryptophan radical. CcP-I is reduced back to the native FeIII state of CcP by two single-electron-transfer reactions with ferrocytochrome c. A second enzyme intermediate called CcP compound II (CcP-II) is produced during the reduction of CcP-I back to CcP. There are two forms of CcP-II, one that retains the FeIV heme group called CcP-IIF and one that retains the tryptophan radical called CcP-IIR. CcP-IIF and CcP-IIR appear to equilibrate via intra-molecular electron transfer but the rate of this step has been difficult to measure with certainty. One of the specific aims of this research proposal is to elucidate the involvement of the CcP-IIF/CcP-IIR equilibrium in the catalytic mechanism of CcP. Cytochrome c and CcP must form a complex in order to transfer electrons and the cytochrome c/CcP system provides an exceptional opportunity to explore details of protein-protein recognition as well as long-range electron transfer within dynamic, electrostatically stabilized protein-protein complexes. Structural aspects of the system are very well characterized with crystal structures available for 1:1 complexes of yeast iso-1 cytochrome c/CcP and horse cytochrome c/CcP, as well as for the individual proteins. A major goal of this research proposal is to determine the factors involved in binding of the two proteins and how these factors govern the specificity of the interaction as well as rapid turnover of the complex. Specificity and rapid turnover have opposite requirements with respect to binding affinity and the enzyme must evolve to optimize both properties simultaneously. The interaction between cytochrome c and CcP is mainly electrostatic in nature. Forty-six charge-reversal mutations on the surface of CcP have been constructed and characterized. The effect of the charge-reversal mutations on cytochrome c binding will be investigated using isothermal titration calorimetry and this data will be used to locate the primary and secondary binding domains. The formation and dissociation rates of the cytochrome c/CcP complex will be determined during the project.

Public Health Relevance

One of the fundamental organizing principles of life is the requirement for the interaction of proteins with other biological molecules. The research described in this proposal is designed to explore details of protein-protein recognition in the cytochrome c/CcP system where both specificity and rapid turnover are required for function. The relevance of this research project to public health is to further our basic understanding of specific protein-protein interactions that could lead to the development of therapeutics to modulate aberrant protein-protein interactions involved in disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Academic Research Enhancement Awards (AREA) (R15)
Project #
2R15GM059740-04A1
Application #
7636698
Study Section
Macromolecular Structure and Function A Study Section (MSFA)
Program Officer
Anderson, Vernon
Project Start
1999-07-01
Project End
2013-12-31
Budget Start
2009-04-01
Budget End
2013-12-31
Support Year
4
Fiscal Year
2009
Total Cost
$211,200
Indirect Cost
Name
Northern Illinois University
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
001745512
City
De Kalb
State
IL
Country
United States
Zip Code
60115
Bidwai, Anil; Ayala, Caitlan; Vitello, Lidia B et al. (2015) Apolar distal pocket mutants of yeast cytochrome c peroxidase: Binding of imidazole, 1-methylimidazole and 4-nitroimidazole to the triAla, triVal, and triLeu variants. Biochim Biophys Acta 1854:919-29
Bidwai, Anil K; Ahrendt, Angela J; Sullivan, John S et al. (2015) pH dependence of cyanide and imidazole binding to the heme domains of Sinorhizobium meliloti and Bradyrhizobium japonicum FixL. J Inorg Biochem 153:88-102
Erman, James E; Vitello, Lidia B; Pearl, Naw May et al. (2015) Binding of Yeast Cytochrome c to Forty-Four Charge-Reversal Mutants of Yeast Cytochrome c Peroxidase: Isothermal Titration Calorimetry. Biochemistry 54:4845-54
Erman, James E; Chinchilla, Diana; Studer, Jason et al. (2015) Binding of imidazole, 1-methylimidazole and 4-nitroimidazole to yeast cytochrome c peroxidase (CcP) and the distal histidine mutant, CcP(H52L). Biochim Biophys Acta 1854:869-81
Chinchilla, Diana; Kilheeney, Heather; Vitello, Lidia B et al. (2014) Kinetic and equilibrium studies of acrylonitrile binding to cytochrome c peroxidase and oxidation of acrylonitrile by cytochrome c peroxidase compound I. Biochem Biophys Res Commun 443:200-4
Bidwai, Anil K; Meyen, Cassandra; Kilheeney, Heather et al. (2013) Apolar distal pocket mutants of yeast cytochrome c peroxidase: hydrogen peroxide reactivity and cyanide binding of the TriAla, TriVal, and TriLeu variants. Biochim Biophys Acta 1834:137-48
Erman, James E; Kilheeney, Heather; Bidwai, Anil K et al. (2013) Peroxygenase activity of cytochrome c peroxidase and three apolar distal heme pocket mutants: hydroxylation of 1-methoxynaphthalene. BMC Biochem 14:19
Foshay, Miriam C; Vitello, Lidia B; Erman, James E (2011) Effect of alternative distal residues on the reactivity of cytochrome c peroxidase: properties of CcP mutants H52D, H52E, H52N, and H52Q. Biochim Biophys Acta 1814:525-35
DiCarlo, Cory M; Vitello, Lidia B; Erman, James E (2011) Reduction potential of yeast cytochrome c peroxidase and three distal histidine mutants: dependence on pH. J Inorg Biochem 105:532-7
Foshay, Miriam C; Vitello, Lidia B; Erman, James E (2009) Relocation of the distal histidine in cytochrome c peroxidase: properties of CcP(W51H), CcP(W51H/H52W), and CcP(W51H/H52L). Biochemistry 48:5417-25

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