C-reactive Protein Molecules Research Articles

Augmentation of 1-0-alkyl-2-0-acetyl- [formula omitted]-glycero-3-phosphocholine(PAF)-induced human platelet activation by C-reactive protein

Activation of human platelets by PAF was augmented by C-reactive protein, an acute phase plasma protein. The concentration of PAF required for irreversible activation (secondary aggregation of platelet and release of serotonin) was decreased to 1/10 in the presence of C-reactive protein (CRP). The presence of CRP stimulated ADP-induced activation, whereas CRP has no effect on collagen-induced activation. Human CRP affected only human platelets, but not rabbit or guinea pig platelets. The conformational modification in CRP molecule was required for the augmentation effect, since the activity was acquired only when CRP was freeze-thawed. Conformational change of CRP on freezing and thawing was observed on CD spectrum of the protein. CRP also augmented the activation of human peripheral polymorphonuclear cells by PAF.

Antigenic, electrophoretic and binding alterations of human C-reactive protein modified selectively in the absence of calcium

C-Reactive protein (CRP) is a trace component of normal human serum which has a mol. wt of 105,000 and is composed of five apparently identical subunits arranged in cyclic symmetry. The serum concentration of this protein is known to increase dramatically in response to acute inflammatory or necrotic processes. We report here that in the presence of high concentrations of urea significant antigenic, electrophoretic and binding site modifications of CRP occur selectively in the absence of calcium. CRP treated in this way (designated F-CRP) had a pI of 5.4 and α-electrophoretic mobility in contrast to the native molecule which had a pI of 6.4 and γ-mobility. F-CRP retained a partial antigenic identity to native CRP, displayed decreased intrinsic tryptophan fluorescence, and expressed a new antigenic reactivity. A similar neoantigen was expressed by heating CRP selectively in the absence if calcium (63°C, 5 min). Treatment with guanidinium-HCl or deliberate carbamylation did not produce F-CRP or the expression of the F-antigen. The formation of F-CRP in urea or by heat was prevented by the presence of 0.7 m M or more calcium. CRP treated in this way retained identical characteristics to native CRP. F-CRP chromatographed through Sephadex G-150 in the presence or absence of 6 M urea as a protein of apparent mol. wt 75,000 with no evidence for free CRP subunits. The formation of F-CRP from native CRP resulted in a loss of capacity for calcium-dependent binding to the C-polysaccharide despite the persistence of calcium-independent binding reactivity for polycations. These data suggest that in the presence of sufficient calcium CRP can resist urea- or heat-induced structural denaturation, maintaining antigenic, electrophoretic and binding identity to the native molecule. In the absence of calcium, exposure to urea led to increased electrophoretic mobility and exposure of a new antigenic reactivity, and to alterations in the phosphocholine- but not the polycation-binding sites of the native CRP molecule; this new antigenic reactivity may be of value in further studies on the CRP molecule.

Primary structure of human C-reactive protein.

The complete amino acid sequence has been derived for human C-reactive protein (CRP). The protein yielded a unique sequence containing 187 amino acids in a single polypeptide chain. The NH2-terminal residue of CRP is pyrrolidonecarboxylic acid and the COOH terminus is proline. The 2 half-cystine residues at positions 36 and 78 are involved in a disulfide bond. Based on the amino acid composition derived from the sequence data, a minimal molecular weight of 20,946 has been calculated for human CRP. This value agrees well with the molecular weight of 21,500 established by gel filtration of CRP in 5.0 M guanidine Cl (Gotschlich, E.C., and Edelman, G.M. (1965) Proc. Natl. Acad. Sci. U.S.A. 54, 558--566). The primary structure of human CRP has been examined for internal homology and compared to all known proteins whose structures were published before April, 1978 by two computer programs; program SEARCH and program RELATE (Dayhoff, M. O., ed (1976) in Atlas of Protein Sequence and Structure, Vol. 5, Suppl. 2, pp. 3--8, National Biomedical Research Foundation, Silver Spring, MD). The computer analyses showed no significant repeating sequences within the C-reactive protein molecule. This observation seems to rule out the possibility of gene duplication in the evolution of this protein. Distant homologies, which were statistically insignificant, have been noted to the CH2 domain of immunoglobulin G (IgG) and to C3a anaphylotoxin. The homologie noted are insufficient to support a common evolutionary origin of these proteins. No homology region in other heavy chains was observed. It is therefore preferable, at this point in time, to assign CRP and the protein known as 9.5 S alpha-glycoprotein, P component, and Clt to a new super family unrelated to any other proteins investigated. The homology between these proteins was demonstrated previously (Osmand, A.P., Friedenson, B., Gewurz, H., Painter, R.H., Hofmann, T., and Shelton, E. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 739--743) on the basis of sequence data on approximately 20 NH2-terminal residues of rabbit C-reactive protein, of Clt, and a cyanogen bromide fragment of human CRP.