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

The relation between structure and specificity of antibodies has been explored by ^(19)F NMR studies of the binding of trifluoromethyl analogues of nitrophenyl haptens to the three mouse myeloma immunoglobulins M315, M460, and X25. We have used haptens with trifluoromethyl groups located at the ortho or para positions of the phenyl ring or attached to the side chain, two atoms removed from the ring (i.e., -NHCH_2CF_3). The changes in chemical shift between hapten free in solution and bound to antibody are sensitive to microenvironment and range from 1.7-ppm downfield to 1-ppm upfield. The shifts of p-trifluoromethylnitrophenyl haptens bound to M315 and M460 are both large downfield shifts, which are likely caused by van der Waals interaction and ring-current effects, particularly from tyrosine-34 (L); these haptens do 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 are observed and their origins considered. The importance of hydrogen bonding in the thermodynamic affinity of antibody for hapten has been estimated by comparisons of binding affinities for haptens with trifluoromethyl groups in place of nitro groups