Analysis of Binding Sites in Human C-reactive Protein for FcγRI, FcγRIIA, and C1q by Site-directed Mutagenesis

Department of Veterans Affairs Medical Center and the University of New Mexico, School of Medicine, Albuquerque, New Mexico 87108, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 08/2005; 280(26):25095-102. DOI: 10.1074/jbc.M504782200
Source: PubMed


Human C-reactive protein (CRP) is a classical, acute phase serum protein synthesized by the liver in response to infection,
inflammation, or trauma. CRP binds to microbial antigens and damaged cells, opsonizes particles for phagocytosis and regulates
the inflammatory response by the induction of cytokine synthesis. These activities of CRP depend on its ability to activate
complement and to bind to Fcγ receptors (FcγR). The goal of this study was to elucidate amino acid residues important for
the interaction of CRP with human FcγRI (CD64) and FcγRIIa (CD32). Several mutations of the CRP structure were studied based
on the published crystal structure of CRP. Mutant and wild-type recombinant CRP molecules were expressed in the baculovirus
system and their interactions with FcγR and C1q were determined. A previous study by our laboratory identified an amino acid
position, Leu176, critical for CRP binding to FcγRI and work by others (Agrawal, A., Shrive, A. K., Greenhough, T. J., and Volanakis, J. E.
(2001) J. Immunol. 166, 3998-4004) determined several residues important for C1q binding. The amino acid residues important to CRP binding to
FcγRIIa were previously unknown. This study newly identifies residues Thr173 and Asn186 as important for the binding of CRP to FcγRIIa and FcγRI. Lys114, like Leu176, was implicated in binding to FcγRI, but not FcγRIIa. Single mutations at amino acid positions Lys114, Asp169, Thr173, Tyr175, and Leu176 affected C1q binding to CRP. These results further identify amino acids involved in the binding sites on CRP for FcγRI, FcγRIIa,
and C1q and indicate that these sites are overlapping.

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Available from: Kevin Du Clos, Jan 06, 2016
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    • "Furthermore, as it protects against the damaging inflammatory response to lipopolysaccharide and cytokines, it may prevent the lethal side-effects of bacterial products [72]. The recent identification of the interaction of CRP with FcγR will lead to an enhanced understanding of CRP and its role in both the innate and acquired immune systems [19,71]. "
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    ABSTRACT: C-reactive protein (CRP) is a nonspecific, acute-phase protein that rises in response to infectious and non-infectious inflammatory processes. Infections are the single largest cause of neonatal deaths globally.The primary aim of this study is to examine the association between CRP gene polymorphism and serum levels of CRP in correlation with early onset sepsis (EOS) infection in newborns living in Taif city, Saudi Arabia. The second aim is to examine the relationship between specific IgG/IgG subclasses and early onset sepsis (EOS) infection among these newborns. Staphylococcus aureus (S. aureus) is one of the most common organisms related to sepsis infection in the newborn at King Abdel Aziz Specialist Hospital (KAASH). This study was conducted in Taif city, at KAASH's neonatal intensive care unit between March and August 2012. Neonates were consecutively enrolled onto the study having met our inclusion criteria (as per our research protocol).The CRP concentration level was analysed using NycoCard(R) CRP Single Test. CRP -286 C >; T > A polymorphisms were analyzed using Pyrosequencing technology for CRP genotyping. IgG subclasses were analysed in the study population using ELISA.Result: Logistic regression analyses showed that the AA and AC genotypes were negatively associated amongst EOS neonates compared to suspected neonates. The frequency of CC and CT were significantly associated with the EOS neonates compared to the suspected group. The levels of specific IgG1, IgG2 and IgG3 antibodies were significantly lower amongst EOS compared to the suspected group. Taken together, the CRP-286 C < T < A genotype polymorphism and specific IgG antibodies isotype levels can contribute to a reduced risk of EOS. Furthermore, CRP has a potential use in detecting EOS in neonates, which may mean earlier detection and management of EOS and subsequently better clinical outcome.
    Full-text · Article · Aug 2013 · BMC Immunology
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    • "In this study we have shown that CRP forms a stable complex with LPC, a major PC-containing phospholipid in oxLDL, supporting our previous observations that exposure of the PC head group of unsaturated fatty acids following oxidation is a prerequisite for binding to CRP [8]. Previous studies have described how two Ca2+ binding sites in the CRP pentamer [18] directly bind to two oxygen atoms within a phosphate group of PC [19], while specific binding sites for FcγRs are located on the opposite plane of CRP [20]. Electron microscopy studies have demonstrated that binding of CPR to PC-containing ligands, including LPC, induces the partial dissociation of the pentameric structure of CRP to an open-ring-like structure [21]. "
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    ABSTRACT: Rationale C-reactive protein (CRP) and lysophosphatidylcholine (LPC) are phosphorylcholine-(PC)-containing oxidized phospholipids (oxPLs) found in oxidized LDL (oxLDL), which trigger pro-atherogenic activities of macrophages during the process of atherosclerosis. It has been previously reported that CRP binds to the PC head group of oxLDL in a calcium-dependent manner. The aim of this study was to investigate the importance of binding between CRP and LPC to the pro-atherogenic activities of macrophages. Objectives and findings A chemiluminescent immunoassay and HPLC showed that human recombinant CRP formed a stable complex with LPC in the presence of calcium. The Kd value of the binding of the CRP-LPC complex to the receptors FcγRIA or FcγRIIA was 3–5 fold lower than that of CRP alone. The CRP-LPC complex triggered less potent generation of reactive oxygen species and less activation of the transcription factors AP-1 and NF-kB by human monocyte-derived macrophages in comparison to CRP or LPC alone. However, CRP did not affect activities driven by components of oxLDL lacking PC, such as upregulation of PPRE, ABCA1, CD36 and PPARγ and the enhancement of cholesterol efflux by human macrophages. The presence of CRP inhibited the association of Dil-labelled oxLDL to human macrophages. Conclusions The formation of complexes between CRP and PC-containing oxPLs, such as LPC, suppresses the pro-atherogenic effects of CRP and LPC on macrophages. This effect may in part retard the progression of atherosclerosis.
    Full-text · Article · Oct 2012 · Journal of Inflammation
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    • "C-reactive protein (CRP) is an acute phase protein, the levels of which increase rapidly in the circulation during infection and/or inflammation. CRP has the ability to activate various immune cells and has also shown a possible capacity to bind to certain FcγR [9]. Fc receptors are widely expressed on leukocytes and they are important players in the immune response, the binding of antibodies to these receptors leading to activation and onset of many important biological events [10]. "
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    ABSTRACT: C-reactive protein (CRP) is an acute phase protein that can activate various immune cells and bind to certain Fcgamma receptors. The latter may compete with the binding of IgG antibodies to these receptors and could thereby interfere with the antigen-specific immune response. Polymorphisms in the promoter region of the CRP gene have been strongly associated with the plasma concentration of CRP. The known lower susceptibility to malaria in the Fulani ethnic group, as compared to their sympatric neighbours in Africa, has been linked to different genetic backgrounds. The present study was performed to investigate if polymorphisms in the CRP gene could contribute to the lower susceptibility to malaria seen in the Fulani ethnic group. The CRP -717 T>C, -286 C>T>A, and +1444 C>T polymorphisms were analysed in asymptomatic Fulani and non-Fulani individuals from Mali and Sudan using Pyrosequencing T and TaqMan r MGB probes. The rare -286 A allele, previously shown to be associated with increased CRP expression and plasma levels, was shown to be more frequent in the non-Fulani ethnic groups as compared to the sympatric Fulani ethnic group both in Mali and Sudan. The common -717 T allele was more prevalent in the non-Fulani ethnic group compared to the sympatric Fulani ethnic group, but only in Mali. The parasite prevalence was increased for the -286 A allele, but not for the -717 T allele. No differences regarding genotype frequency or parasite prevalence were seen for +1444 C>T. This study indicate that CRP may play an important role in the immune responses to malaria, and that the -286 C/T/A CRP polymorphism may be a contributing factor to the lower susceptibility to malaria seen in the Fulani.
    Full-text · Article · Jun 2009 · Malaria Journal
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