Binding of low density lipoprotein (LDL) to C-reactive protein (CRP): a possible binding through apolipoprotein B in LDL at phosphorylcholine-binding site of CRP.

Healthy human serum reacted with C-reactive protein of human (hCRP) or rat (rCRP) immobilized on Sepharose 4B in the presence of Ca2+. The bound serum proteins were eluted with 0.1 M ethylenediaminetetraacetic acid, trisodium salt (EDTA) dissolved in 10 mM Tris-HCl buffer, pH 8.0, containing 140 mM NaCl. The eluted proteins from the hCRP column was found to be low density lipoprotein (LDL), 90% of its protein being apo B. The one from the rCRP column contained also apo B by 36.7%. The effect of phosphorylcholine (PC), phosphorylethanolamine, phosphorylserine, galactose and high density lipoprotein (HDL) on the binding of LDL and apo B to CRP was investigated by enzyme-linked immunosorbent assay. Among them, only PC strongly inhibited the binding. One of the two available mouse monoclonal antibodies to hCRP (#19), which interferes with the binding of PC to CRP molecule, prevented CRP from binding LDL or apo B. In contrast, the other antibody (#17), which does not affect the binding of PC to CRP, did not inhibit the binding of LDL or apo B to CRP. It was therefore concluded that LDL binds to CRP by apo B moiety at the PC-binding site of CRP molecule.