Serum amyloid p component does not circulate in complex with C4-binding protein, fibronectin or any other major protein ligand

Glycosaminoglycan Neutralization in Coagulation Control

The glycosaminoglycans (GAGs) heparan sulfate, dermatan sulfate, and heparin are important anticoagulants that inhibit clot formation through interactions with antithrombin and heparin cofactor II. Unfractionated heparin, low-molecular-weight heparin, and heparin-derived drugs are often the main treatments used clinically to handle coagulatory disorders. A wide range of proteins have been reported to bind and neutralize these GAGs to promote clot formation. Such neutralizing proteins are involved in a variety of other physiological processes, including inflammation, transport, and signaling. It is clear that these interactions are important for the control of normal coagulation and influence the efficacy of heparin and heparin-based therapeutics. In addition to neutralization, the anticoagulant activities of GAGs may also be regulated through reduced synthesis or by degradation. In this review, we describe GAG neutralization, the proteins involved, and the molecular processes that contribute to the regulation of anticoagulant GAG activity.

Antibody-array interaction mapping, a new method to detect protein complexes applied to the discovery and study of serum amyloid P interactions with kininogen in human plasma

Protein-protein interactions are fundamentally important in biological processes, but the existing analytical tools have limited ability to sensitively and precisely measure the dynamic composition of protein complexes in biological samples. We report here the development of antibody-array interaction mapping (AAIM) to address that need. We used AAIM to probe interactions among a set of 48 proteins in serum and found several known interactions as well potentially novel interactions, including multiprotein clusters of interactions. A novel interaction initially identified between the innate immune system protein C-reactive protein and the inflammatory protein kininogen (KNG) was confirmed in subsequent experiments to involve serum amyloid P instead of its highly related family member, C-reactive protein. AAIM was used in a variety of formats to further study this interaction. In vitro studies confirmed the ability of the purified proteins to interact and revealed a zinc dependence of the interaction. Studies using plasma samples collected longitudinally following a controlled myocardial infarction revealed no consistent changes in the serum amyloid P-KNG interaction levels but consistent changes in KNG activation and interactions with plasma prekallikrein. These results demonstrate a versatile platform for measuring the dynamic composition of protein complexes in biological samples that should have value for studies of normal and disease-related signaling networks, multiprotein clusters, or enzymatic cascades.

Proteomic analysis of protein adsorption: Serum amyloid P adsorbs to materials and promotes leukocyte adhesion

Serum and plasma protein adsorption on materials was analyzed using gel electrophoresis and ion trap mass spectrometry. Following incubation of polypropylene, polyethylene terephthalate (PET), or polydimethylsiloxane (PDMS) with 5% serum for longer than 4 h, we found unexpectedly high amounts of the pentraxin serum amyloid P. It was previously shown that serum amyloid P is constitutively expressed in humans, functions as an opsonin, and interacts with the Fcgamma receptors on leukocytes. We demonstrate that serum amyloid P adsorbed to tissue culture polystyrene, PDMS, and PET promotes the adhesion of granulocytes and monocytes in the presence of calcium. The methods developed for these studies may be useful for the large-scale study of protein adsorption and do not rely on radiolabeling or the availability of antibodies.

Structural, quantitative and functional comparison of amyloid P component in sera from patients with systemic lupus erythematosus and healthy donors

Serum amyloid P component (SAP) is a serum protein that has a function as opsonin and is known to bind nuclear material with high affinity. Quantitative and/or qualitative deficiencies in SAP may possibly lead to the impairment of normal homoeostatic mechanisms of tissue turnover. Thus, SAP knockout mice display systemic lupus erythematosus (SLE)-like manifestations such as nephritis and circulating antinuclear antibodies. In the present study, we investigated whether there are changes in the structure, function or serum levels of SAP in serum from SLE patients as compared with those from healthy donors. We found that SAP in SLE sera has the same molecular mass as that of in the sera of normal individuals, when analysed by online immunoaffinity reversed phase mass spectrometry. Also, the serum levels of SAP did not differ significantly between the two groups. Finally, as an estimate of function, SAP from SLE patients appeared to have the same affinity for heparin and nucleosomes as SAP from normal individuals, when analysed by crossed affinity immunoelectrophoresis and enzyme-linked immunosorbent capture assay (ELISA). In conclusion, the data do not support alterations in the levels, structure or function of SAP circulating in SLE patients.