Binding of C-reactive protein to C-carbohydrate and PC-substituted protein

Phosphocholine-Decorated PPI-Dendrimers Mimic Cell Membrane Phosphocholine Clusters and Tune the Innate Immune Activity of C-Reactive Protein

C-reactive protein (CRP) is widely used as biomarkers of infection and inflammation. It has a well-described ability to bind phosphocholine (PC), as well as PC-clusters from compromised and inflamed cell membranes and tissues. The binding of PC-clusters to CRP is of interest as this binding determines subsequent innate immune activity. We investigated PC-decorated dendrimers as mimics for PC-clusters. Five generations of poly(propylene imine) (PPI) dendrimers were modified with PC surface groups via a three-step synthetic sequence obtaining the PC-decorated dendrimers in high purity. The dendrimers were analyzed by NMR and infrared spectroscopy as well as HPLC. We developed immunoassays to show that dendrimer-PC binding to CRP was Ca²⁺-dependent with an apparent overall K_d of 11.9 nM for first generation (G1) PPI-PC, while G2-PPI-PC and G3-PPI-PC had slightly higher affinities, and G4-PPI-PC and G5-PPI-PC had slightly lower affinities. For all PC-dendrimers, the affinity was orders of magnitude higher than the affinity of free phosphocholine (PC), indicating a PC-cluster effect. Next, we investigated the binding of CRP:PPI-PC complexes to complement component C1q. C1q binding to CRP was dependent on the generation of PPI-PC bound to CRP, with second and third generation PPI-PCs leading to the highest affinity. The dendrimer-based approach to PC-cluster mimics and the simple binding assays presented here hold promise as tools to screen PC-compounds for their abilities to tune the innate immune activity of CRP.

Multiple gene and transcript variants encoding trout C-polysaccharide binding proteins are differentially but strongly induced after infection with Aeromonas salmonicida

Two 'trout C-polysaccharide-binding proteins,' TCBP1 and -2, with relevance to early inflammatory events have been discovered in the last century. The present study characterises the respective cDNA sequences from rainbow trout (Oncorhynchus mykiss), including multiple TCBP1 transcript variants. These variants are generated either by the use of alternative splice sites or the exclusion of exons. The longest mRNA isoform, TCBP1-1, encodes a 245-aa protein with a large signal peptide and a complement component C1q domain. The shortest mRNA isoform, TCBP1-5, contains a premature termination codon and hence fails to encode a functional factor. The 224-aa-long TCBP2 protein consists of a comparably shorter signal peptide and a pentraxin domain. Evolutionary analyses clearly separated TCBP1 and -2 because of distinctive protein motifs. Expression profiling in the liver, spleen, and head kidney tissues of healthy trout revealed that TCBP2 mRNA concentrations were higher than the concentrations of all five TCBP1 mRNA isoforms together. The hepatic levels of these TCBP1 variants increased significantly upon infection with Aeromonas salmonicida, whereas TCBP2 transcript levels rose moderately. As the biological function of TCBP1 is barely understood, we tagged this factor with the green fluorescent protein and visualised its expression in HEK-293 cells. Overexpression of TCBP1 increased the level of active NF-κB factors and induced cell death, indicating its involvement in proapoptotic NF-κB-dependent signalling routes.

Serum amyloid P aids complement-mediated immunity to Streptococcus pneumoniae

The physiological functions of the acute phase protein serum amyloid P (SAP) component are not well defined, although they are likely to be important, as no natural state of SAP deficiency has been reported. We have investigated the role of SAP for innate immunity to the important human pathogen Streptococcus pneumoniae. Using flow cytometry assays, we show that SAP binds to S. pneumoniae, increases classical pathway–dependent deposition of complement on the bacteria, and improves the efficiency of phagocytosis. As a consequence, in mouse models of infection, mice genetically engineered to be SAP-deficient had an impaired early inflammatory response to S. pneumoniae pneumonia and were unable to control bacterial replication, leading to the rapid development of fatal infection. Complement deposition, phagocytosis, and control of S. pneumoniae pneumonia were all improved by complementation with human SAP. These results demonstrate a novel and physiologically significant role for SAP for complement-mediated immunity against an important bacterial pathogen, and provide further evidence for the importance of the classical complement pathway for innate immunity.

Serum amyloid P (SAP) is a protein that is found in high concentrations in the blood, the exact function(s) of which are not clear. However, no known natural state of SAP deficiency has been identified, which suggests that SAP does have a vital role in human health. SAP can bind to molecular patterns found on the surface of bacteria, and it has been proposed that this may mark bacteria for attack by the immune system. We have investigated whether SAP helps protect against an important bacterial pathogen, Streptococcus pneumoniae. We show that SAP binds to different strains of S. pneumoniae, and that this leads to activation of an important component of the immune response called the complement system. Complement is particularly important for defence against S. pneumoniae infections, and using animal models of infection, we demonstrate that loss of SAP makes mice more susceptible to S. pneumoniae pneumonia. These results suggest that SAP helps the immune system to recognise invasion by bacteria and describe a new mechanism required for control of S. pneumoniae infections. This study may help the design of new therapeutic strategies to prevent or treat important bacterial diseases.

Carbohydrate ligands of human C-reactive protein: binding of neoglycoproteins containing galactose-6-phosphate and galactose-terminated disaccharide

Binding of carbohydrate ligand by human C-reactive protein (CRP), in both native form and structurally deviated form (neoCRP or mCRP), was investigated using galactose-6-phosphate (Gal6P)- and Galbeta3GalNAc-containing bovine serum albumin (BSA) derivatives. To this end, we synthesized glycosides of Gal6P and Galbeta3GalNAc that can potentially generate a terminal aldehyde group. omega-Aldehydo glycosides were then conjugated to BSA via reductive amination. Using these neoglycoproteins, we showed that: (1) Gal6P-BSA and Galbeta3GalNAc-BSA bound to both forms of CRP, the former with or without calcium and the latter only in the absence of calcium; (2) phosphate-containing ligands can be bound with or without calcium, but the binding is much stronger in the presence of calcium than in the absence, underscoring the importance of direct coordination of phosphate to two calcium ions observed in the X-ray structure of phosphorylcholine (PC)-CRP complex; (3) cross-inhibition studies further corroborated the hypothesis that binding sites of PC and sugar are contiguous; (4) while PC-BSA bound to the native CRP over a wide pH range of 4.5 to 9, all the carbohydrate ligands and protamine-BSA (poly-cation-based ligand) exhibited optimal binding at around pH 6 to 6.5; and (5) ligand-binding conformation of mCRP appears to be more fragile than that of the native CRP in the acidic media (pH < 6).

High sensitivity C-reactive protein: an emerging role in cardiovascular risk assessment

Coronary heart disease (CHD) is the major cause of death in the developed world and screening for conventional cardiovascular risk factors fails to identify more than 50% of the individuals who will present with acute coronary syndromes. Chronic inflammation appears to play a significant role in the initiation and development of atherosclerosis. Recent investigations have shown an association between inflammatory markers such as C-reactive protein (CRP) and CHD. These markers have proven useful as prognostic indicators in acute coronary syndromes and in predicting future coronary events in apparently healthy men and women. The availability of high sensitivity CRP (hs-CRP) assays has been crucial in exploring the role of this acute phase reactant in primary prevention settings. In this review, we discuss the evidence associating these inflammatory markers, especially CRP, with the pathogenesis of atherosclerosis and acute coronary syndromes, and we address the mechanism of risk as well as the clinical utility of this marker.

Immunohistochemical localization of modified C-reactive protein antigen in normal vascular tissue

BACKGROUND

The prototypic acute phase reactant, C-reactive protein (CRP), is a serum soluble, cyclic pentameric protein, the concentration of which increases markedly within hours of any tissue-damaging, inflammatory event. However, upon dissociation of its pentameric quaternary structure, CRP subunits undergo a spontaneous and irreversible conformational change. The resulting molecule, termed modified CRP or mCRP, has reduced aqueous solubility and a propensity to aggregate into a matrix-like lattice structure.

METHODS

Using monoclonal antibodies, normal human tissues were immunohistochemically screened for the presence of CRP as well as mCRP antigens.

RESULTS

Significant levels of mCRP were detected in the walls of blood vessels associated with normal human tissues. These data indicate that mCRP is a naturally occurring form of CRP and that it is a tissue-based rather than serum-based molecule.

SIGNIFICANCE

This report describes the localization of a stable form of CRP, mCRP, in blood vessels associated with normal human tissues.

Lectin like properties and differential sugar binding characteristics of C-reactive proteins purified from sera of normal and pollutant induced Labeo rohita

Different forms of C-reactive proteins (CRPs) have been purified to electrophoretic homogeneity from the sera of Labeo rohita confined in freshwater (CRP(N)) and water polluted with nonlethal doses of cadmium (CRP(Cd)) or mercury (CRP(Hg)). CRP(N), CRP(Cd), and CRP(Hg) show remarkable differences in their electrophoretic mobility but exhibit strong immunological cross reactivity. All these CRPs exhibit variable agglutination properties with erythrocytes from diverse sources in presence of Ca+2, which could be inhibited by a variety of sugars showing specificity for galactose. Inhibition results show that the potency of galactose as an inhibitor increases about 4 fold in the process of transformation of CRP(N) to CRP(Cd) and CRP(Hg). In case of CRP(N), Gal beta(1 --> 1) Gal and oNO2 phenyl beta-Gal show highest inhibitory potency while oNO2-phenyl beta-Gal is the most potent inhibitor for CRP(Cd) and CRP(Hg) but the potency of Gal beta(1 --> 1) Gal reduced drastically. 6-phosphate D-Gal and stachyose are 20 times weaker inhibitors than D-Gal for induced CRP mediated agglutination, in contrast, these sugars are only 6 times weaker for CRP(N). Dissociation constants of the binding of CRP(N) with phosphoryl choline (PC) and galactose are about 9 mM and PC binding causes a change in the alpha and beta conformations of these CRPs.

Levels of C-reactive protein in serum samples from healthy children and adults in São Paulo, Brazil

C-reactive protein (CRP) was measured by ELISA in the sera of 165 healthy blood donors and 125 normal children 1 to 14 years old. The serum levels of blood donors ranged from 0.05 to 57.6 mg/l with median and mean values of 1.8 mg/l and 4.86 mg/l, respectively. CRP levels ranged from 0.02 to 14.4 mg/l in the children's sera, the median being 0.45 mg/l and the mean 1.65 mg/l. No individual lacking CRP was detected. The high CRP levels observed in the present study suggest that the population of the State of São Paulo may usually be exposed to subacute infections and/or inflammation without presenting clinical symptoms.

Association of rat C-reactive protein and other pentraxins with rat lipoproteins containing apolipoproteins E and A1

C-Reactive protein (CRP) is a member of the pentraxin family of proteins, ubiquitous components of animal serum. This study suggests that, in serum, rat CRP is complexed with lipoprotein and may interact directly with apolipoprotein E. When mixed with diluted rat serum, radiolabeled rat CRP showed a slightly higher sedimentation coefficient (about 15%) than that of the free protein. Elimination of calcium or addition of O-phosphorylethanolamine (O-PE), a low molecular weight compound that binds tightly to rat CRP in a calcium-dependent manner, abolished this difference. Adsorption of rat serum on a rat CRP affinity gel and elution with PE resulted in the isolation of material containing high levels of apolipoproteins E and A1. The affinity-purified preparation interacted with rat CRP and altered the sedimentation coefficient of the latter to the value observed in whole serum. Conversely, rat CRP increased the sedimentation coefficient of the major component of the affinity-purified material or to diluted rat serum, human serum amyloid P (SAP) and hamster female protein (FP), two other members of the pentraxin protein family, also had slightly higher sedimentation coefficients. In contrast, human CRP showed no evidence of an interaction in rat serum or with the affinity-purified proteins. This selectivity coincided with the ability of these pentraxins to bind to O-PE with high affinity. The sedimentation properties of serum lipoproteins, radiolabeled with [3H]cholesterol, also suggested an interaction with rat CRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentraxin family of proteins interact specifically with phosphorylcholine and/or phosphorylethanolamine

Pentraxins are a family of serum proteins characterized by five identical subunits that are noncovalently linked. The two major types of pentraxins are C-reactive protein (CRP) and serum amyloid P component (SAP). CRP proteins are identified by their calcium-dependent interaction with phosphorylcholine. This study showed that SAP also bound to phosphorylated compounds but had a high specificity for phosphorylethanolamine. Thus, human CRP and SAP show high specificity that is complementary for the related compounds, phosphorylcholine and phosphorylethanolamine, respectively. This relationship suggests a complementary and/or related function for the pentraxins. Pentraxins from other species were also examined. Mouse SAP showed binding interactions and specificity similar to human SAP. Female protein (FP) from hamster and rat CRP showed a hybrid specificity and bound to both phosphorylethanolamine and phosphorylcholine. All of the proteins that bound phosphorylethanolamine also associated with human C4b-binding protein (C4BP). With the exception of human and rat CRP, all the proteins also bound to vesicles containing acidic phospholipids. All of these binding interactions were calcium-dependent and mutually exclusive, suggesting that they involved the same site on the protein. These findings suggest possible ways to examine the function of the pentraxins.

Effects of lipid-binding proteins apo A-I, apo A-IL, beta 2-glycoprotein I, and C-reactive protein on activation of factor X by tissue factor--factor VIIa

Tissue factor is the membrane-associated protein which mediates activation of factors IX and X by factor VII. In a purified, reconstituted bovine system, factor X activation by the tissue factor-factor VIIa complex is inhibited by the mixed apoproteins from human high density lipoprotein (HDL) and by isolated apolipo-protein A-II (apo A-II). Other proteins found associated with plasma lipoproteins, apolipoprotein A-I (apo A-I), C-reactive protein (CRP), and beta 2-glycoprotein I (beta 2 GPI), have been examined for effects on the activation of factor X by tissue factor-factor VIIa. In these experiments, bovine tissue factor, reconstituted into phosphatidylserine-phosphatidylcholine (PS/PC; 30/70) vesicles, was used at a single concentration while factor X (the substrate), factor VIIa (the enzyme), and the potentially inhibitory proteins were varied in a continuous chromogenic assay. Apo A-II and CRP clearly inhibit tissue factor-factor VIIa activation of factor X, while apo A-I and beta 2 GPI have little or no effect. These results demonstrate that different lipid binding proteins vary in their effects on tissue factor activity.

Comparative studies of serum and synovial fluid C reactive protein concentrations

The relation between serum and synovial fluid (SF) C reactive protein (CRP) concentrations was investigated in a variety of arthritides, including rheumatoid arthritis (RA), psoriatic arthritis, reactive arthritis, and osteoarthritis. SF CRP levels were significantly reduced compared with serum levels in the inflammatory arthritides, but there was good correlation between serum and SF values. SF CRP values were all at the lower limit of the detectable range in osteoarthritis. In patients with RA or psoriatic arthritis followed up serially through an exacerbation of arthritis, changes in SF CRP reflected closely changes in serum CRP. In patients with RA SF/serum ratios of proteins of different molecular weight were used to derive a regression equation between SF/serum ratio and molecular mass. SF/serum values for CRP were significantly less than predicted from its molecular weight, suggesting that CRP is either being selectively bound in synovium or specifically consumed in SF and may be playing an important part in the inflammatory process in RA.

Immunohistochemical studies of C-reactive protein and apolipoprotein B in inflammatory and arterial lesions

Interactions in vivo between C-reactive protein (CRP) and apolipoprotein B (apo-B)-containing lipoproteins were sought in inflammatory lesions and atherosclerosis. CRP was demonstrated immunohistochemically on the surface of some muscle fibres in locally induced inflammatory lesions in the rabbit, but apoB was not detected in the same distribution. CRP was not detected in catheter-induced aortic endothelial injuries in the rabbit, in arterial lesions containing apoB from cholesterol-fed rabbits, in apoB-containing human fatty streaks or in advanced human atherosclerotic lesions.

Evaluation of a C-reactive protein latex agglutination detection test with sera from patients with sexually transmitted diseases

A total of 149 sera, including 79 pre- and posttreatment sera from 33 patients with disseminated gonococcal infections, 18 from patients with uncomplicated gonococcal infections, 6 from patients with pelvic inflammatory disease, 4 from patients with genital Chlamydia trachomatis infections, and 42 from normal volunteers, were examined for C-reactive protein with a latex agglutination C-reactive protein detection kit (Difco Laboratories, Detroit, Mich.). Results were quantitated with LC-Partigen C-reactive protein radial immuno-diffusion plates (Calbiochem-Behring, La Jolla, Calif.). Positive latex agglutination results were observed in all of the pretreatment sera and some of the posttreatment sera of patients with disseminated gonococcal infections and in two sera from patients with pelvic inflammatory disease, which corresponded to quantitative C-reactive protein levels in the radial immunodiffusion plates. C-reactive protein levels were not detectable in the serum samples from normal volunteers or patients with uncomplicated gonococcal infections or genital chlamydial infections. Positive latex agglutination occurred as early as 20 s in sera with high C-reactive protein levels, and all positive results were observed within 90 s of the 3-min test limit. Positive latex test results were obtained with C-reactive protein levels as low as 1 mg/dl (10 micrograms/ml).

Phosphorylcholine determinants in six pneumococcal capsular polysaccharides detected by monoclonal antibody

The presence of phosphorylcholine in pneumococcal capsular polysaccharides was examined by using monoclonal antiphosphorylcholine antibody. Of the 83 known capsular types of Streptococcus pneumoniae, 6 types, viz., 24A, 27, 28F, 28A, 32F, and 32A, gave a positive capsular reaction (quellung) which could be inhibited by phosphorylcholine. The capsular polysaccharides of these six types, therefore, contain phosphorylcholine.

Rabbit and rat C-reactive proteins bind apolipoprotein B-containing lipoproteins

Immobilized rabbit and rat C-reactive protein (CRP) were found to selectively bind apolipoprotein B (apoB)-containing lipoproteins (low density lipoprotein, LDL and very low density lipoprotein, VLDL) from whole serum in a manner similar to that previously reported with human CRP. In acute phase human serum the CRP is in a free form, not complexed with lipoprotein or any other macromolecular ligand, and in acute phase serum from most rabbits fed on a normal diet the rabbit CRP was also free. However, in acute phase serum or heparinized plasma from hypercholesterolemic rabbits part or all of the CRP was found by gel filtration and immunoelectrophoretic techniques to be complexed with beta-VLDL, an abnormal apoB-containing plasma lipoprotein present in these animals. The presence of extent in different serum samples of CRP complexed with lipoprotein correlated closely with the serum apoB concentration. The formation of complexes between native, unaggregated rabbit CRP in solution and apoB-containing lipoproteins was readily demonstrable experimentally both with the isolated proteins and in whole serum. In all cases these interactions were calcium-dependent and inhibitable by free phosphoryl choline. The present findings extend earlier work in man and the rabbit and indicate that among the C-reactive proteins from different species, which are structurally highly conserved, the capacity for selective binding to apoB-containing plasma lipoproteins is also a constant feature. These interactions may therefore be related to the in vivo function of CRP in all species and this function may in turn be relevant to pathological conditions, such as atherosclerosis, in which lipoproteins are important.

Acute phase proteins with special reference to C-reactive protein and related proteins (pentaxins) and serum amyloid A protein

The acute phase response among plasma proteins is a normal response to tissue injury and is therefore a fundamental aspect of many diverse disease processes. It probably usually has a beneficial net function in limiting damage and promoting repair but in some circumstances it may have pathological consequences. Sustained high levels of acute phase proteins and especially SAA are associated with the development of amyloidosis in some individuals. Increased concentrations of CRP may, by activating the complement system, contribute to inflammation and enhance tissue damage. Failure of the normal or appropriate CRP response may also possibly have deleterious effects. SAA is a polymorphic protein which is normally present only in trace amounts but which, during the acute phase response, becomes one of the major apolipoproteins associated with high-density lipoprotein particles. The function of apoSAA is not known but it must have considerable physiological significance apart from its role as the putative precursor of amyloid A protein fibrils. CRP and SAP have been very stably conserved throughout vertebrate evolution and homologous proteins are apparently present even in vertebrates. This strongly suggests that they have important functions although these have not yet been precisely delineated. The main role of CRP may be to provide for enhanced clearance of inappropriate materials from the plasma whether these are of extrinsic origin, such as microorganisms and their products, or the autologous products of cell damage and death. The interaction between aggregated CRP and plasma low-density lipoprotein may play a significant part in the normal function of CRP and may also have a role in lipoprotein metabolism, clearance, and deposition. SAP is a normal tissue protein as well as being a plasma protein. Aggregated SAP selectively binds fibronectin and this may represent an aspect of the normal function of SAP. The deposition of SAP in amyloid is evidently not a normal function but it is not known whether this deposition is involved in the pathogenesis of amyloid or whether it is merely an epiphenomenon. In any case immunohistochemical staining for SAP is useful in the diagnosis of amyloid, in investigation of glomerulonephritis, and in studying disorders of elastic tissue. Regardless of its physiological or pathophysiological functions, the assay of serum CRP is a valuable aid to clinical management in a number of different situations and in different diseases provided results are interpreted in the light of full clinical information.(ABSTRACT TRUNCATED AT 400 WORDS)

Low density lipoprotein and very low density lipoprotein are selectively bound by aggregated C-reactive protein

C-reactive protein (CRP), the classical acute-phase protein, can bind phospholipids by virtue of its specific, calcium-dependent reactivity with phosphorylcholine residues. However, analysis of acute-phase serum by gel filtration and by density gradient ultracentrifugation showed that the CRP was in a free, uncomplexed form, despite the coexistent presence of the various classes of serum lipoproteins, all of which contain phospholipids. In contrast, when isolated CRP was aggregated by immobilization at a sufficient density on a solid phase and then exposed to normal human serum, it selectively bound low density lipoprotein (LDL) and traces of very low density lipoprotein. The reaction was calcium dependent and reversible by free phosphorylcholine but not by heparin. LDL isolated from normal plasma was also bound by aggregated CRP. CRP reacts in vitro with a wide variety of different ligands both of extrinsic and of autogenous origin, e.g., microbial products and damaged cell membranes, respectively. If CRP aggregated in vivo by complexing with these ligands than acquires the capacity to selectively bind LDL, the phenomenon may have significant implications for the function of CRP and for the metabolism, clearance, and deposition of LDL.