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Title: Human serum amyloid P component oligomers bind and activate the classical complement pathway via residues 14-26 and 76-92 of the A chain collagen-like region of C1q. Author: Ying SC, Gewurz AT, Jiang H, Gewurz H. Journal: J Immunol; 1993 Jan 01; 150(1):169-76. PubMed ID: 8417122. Abstract: Serum amyloid P component (SAP) was polymerized using the cleavable cross-linker 3,3'-dithio-bis-(sulfo-succinimidylpropionate) to study its interaction with the C system. Dimers and trimers, but no larger oligomers, were observed; the trimers retained native SAP immunoreactivity (except for one calcium-dependent epitope) without displaying neo-SAP epitopes. The SAP trimers bound strongly to C1q, at the level of the collagen-like region (CLR). SAP bound to synthetic C1q A chain peptides 14-26 and 76-92, and these peptides inhibited the binding of SAP trimers to the CLR. When incubated in dilute human serum, SAP trimers consumed total C and C4, but not alternative pathway, hemolytic activities. Consumption of C4 by SAP trimers was inhibited by C1q A chain peptide 14-26. Thus, SAP oligomers bind C1q and activate the classical C pathway via the collagen-like region of C1q, at sites located within residues 14-26 and/or 76-92 of the C1q A chain.[Abstract] [Full Text] [Related] [New Search]