Localization of the phosphocholine-binding sites on C-reactive protein by immunoelectron microscopy.
C-reactive protein (CRP) was reacted with monoclonal IgG antibody or Fab antibody fragments directed against the phosphocholine- (PC) binding site or a second unrelated site. The resulting immune complexes were viewed by a negative stain immunoelectron microscopy technique. Monoclonal anti-PC-binding site antibody bound to a single epitope on each of the five CRP subunits. The orientation of the PC-binding sites was determined to be slightly medial to one of the planar faces (A-face) of the molecule. The second monoclonal antibody, which was not PC-binding site related, bound to epitopes (one per CRP subunit) that were located slightly lateral to the other planar face (B-face) of the CRP molecule, i.e., opposite of the PC-binding site. Thus, the PC-binding site and the non-PC-binding site are oriented nearly perpendicular but on opposite sides with respect to the plane of the CRP molecule. The functional significance of this configuration is discussed.
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D002097:C-Reactive Protein / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000032:analysis* / Q000378:metabolism; D002794:Choline / Q000031:analogs & derivatives*; D000939:Epitopes / Q000276:immunology; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D051379:Mice; D008855:Microscopy, Electron, Scanning; D010767:Phosphorylcholine / Q000276:immunology / Q000378:metabolism*; D011487:Protein Conformation
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; C030929:Crp protein, rat; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D010767:Phosphorylcholine; D002097:C-Reactive Protein; D002794:Choline