Relation between structure and specificity of antibodies: nuclear magnetic resonance study of binding fluorine-19 labeled nitrophenyl haptens to myeloma immunoglobulins M315, M460, and X25

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Abstract
The relation between structure and specificity of antibodies was explored by 19F NMR studies of the binding of trifluoromethyl analogues of nitrophenyl haptens to the 3 mouse myeloma immunoglobulins, i.e., M315, M460 and X25. The haptens used had trifluoromethyl groups located at the ortho or para positions of the phenyl ring or attached to the side chain, 2 atoms removed from the ring (i.e., -NHCH2CF3). The changes in chemical shift between hapten free in solution and bound to antibody were sensitive to microenvironment and ranged from 1.7 ppm downfield to 1 ppm upfield. The shifts of p-trifluoromethylnitrophenyl haptens bound to M315 and M460 were both large downfield shifts, which were likely caused by van der Waals interaction and ring-current effects, particularly from tyrosine-34 (L); these haptens did not show similar shifts when bound to X25, which has a deletion of tyrosine-34 (L). Other differences in the binding of the aromatic rings of haptens by M315, M460 and X25 were observed and their origins considered. The importance of H bonding in the thermodynamic affinity of antibody for hapten was estimated by comparisons of binding affinities for haptens with trifluoromethyl groups in place of nitro groups.