title: Functional Transformation of C-reactive Protein by Hydrogen Peroxide.
abstract: C-reactive protein (CRP) is present at sites of inflammation including amyloid plaques, atherosclerotic lesions, and arthritic joints. CRP, in its native pentameric structural conformation, binds to cells and molecules that have exposed phosphocholine (PCh) groups. CRP, in its non-native pentameric structural conformation, binds to a variety of deposited, denatured, and aggregated proteins, in addition to binding to PCh-containing substances. In this study, we investigated the effects of H2O2, a prototypical reactive oxygen species that is also present at sites of inflammation, on the ligand recognition function of CRP. Controlled H2O2treatment of native CRP did not monomerize CRP and did not affect the PCh binding activity of CRP. In solid phase ELISA-based ligand binding assays, purified pentameric H2O2-treated CRP bound to a number of immobilized proteins including oxidized LDL, IgG, amyloid β peptide 1-42, C4b-binding protein, and factor H, in a CRP concentration- and ligand concentration-dependent manner. Using oxidized LDL as a representative protein ligand for H2O2-treated CRP, we found that the binding occurred in a Ca2+-independent manner and did not involve the PCh-binding site of CRP. We conclude that H2O2is a biological modifier of the structure and ligand recognition function of CRP. Overall, the data suggest that the ligand recognition function of CRP is dependent on the presence of an inflammatory microenvironment. We hypothesize that one of the functions of CRP at sites of inflammation is to sense the inflammatory microenvironment, change its own structure in response but remain pentameric, and then bind to pathogenic proteins deposited at those sites.
authors.affiliation: Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614.
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Singh
authors.affiliation: Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614.
authors.forename: Avinash
authors.initials: A
authors.lastname: Thirumalai
authors.affiliation: Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614.
authors.forename: Asmita
authors.initials: A
authors.lastname: Pathak
authors.affiliation: Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614.
authors.forename: Donald N
authors.initials: DN
authors.lastname: Ngwa
authors.affiliation: Department of Biomedical Sciences, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614. Electronic address: agrawal@etsu.edu.
authors.forename: Alok
authors.initials: A
authors.lastname: Agrawal
mesh_terms: D001665:Binding Sites; D002097:C-Reactive Protein / Q000737:chemistry / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008024:Ligands; D008077:Lipoproteins, LDL / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization
chemical_list: D008024:Ligands; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D002097:C-Reactive Protein; D006861:Hydrogen Peroxide; D002118:Calcium
keywords: host defense; immunology; inflammation; innate immunity; ligand-binding protein