Magnetic resonance studies of the binding site interactions between phosphorylcholine and specific mouse myeloma immunoglobulin

The interaction of phosphorylcholine-binding mouse myeloma protein M603 and the isotopically substituted hapten phosphoryl[rnethyl-^(13)C]choline has been investigated using ^(13)C and ^(31)P nuclear magnetic resonance (NMR) spectroscopy. Upon binding to antibody, upfield shifts of 0.7 and 1.5 ppm are observed for the hapten ^(13)C and ^(31)P resonances, respectively, and both spectra are in the "slow" exchange limit. Linewidth analysis indicates some immobilization of the phosphate group but essentially unrestricted methyl group rotation for the bound hapten. Hapten-antibody dissociation rate constants of 10 and 38 s^(-1) are calculated from ^(13)C and ^(31)P NMR spectra, respectively, suggesting the possibility of differential dissociation rates for the two opposing ends of the phosphorylcholine molecule. The NMR data are entirely consistent with the known x-ray structure of the M603 Fab'-phosphorylcholine complex (Segal, D. M., Padlan, E. A., Cohen, G. H., Rudikoff, S., Potter, M., and Davies, D.R. (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 4298)