Proton nuclear magnetic resonance studies of human immunoglobulins. Solution conformation of the constant domain of the lambda light chains and identification of the isotypes.

Sixteen lambda-type Bence-Jones proteins and eight constant domain fragments of lambda chains were used to measure nuclear magnetic resonance (NMR) signal of the C2- AND C4-H protons of two histidine residues (His- 189 and His-198) which exist in the constant half of the lambda chains. The pH titration curves for the C2-H proton signals of His-189 and His-198 of six Bence-Jones dimers were compared with those for the corresponding constant fragments. It was concluded that the tertiary structure of the constant domain is well preserved even in the constant fragments which are known to exist as the monomer in solution. It was shown that the C2- and C4-H proton peaks of His-198 can be used to identify the Mcg isotype. It was also shown that the chemical shifts of the C4-H proton of His-189 and His-198 can be used to detect the amino acid substitutions at positions 153 and 190 which are the Kern and Oz markers, respectively. On the basis of the NMR measurements, it was suggested that the Kern and at least one of the Mcg markers are in close spatial proximity to His-189 and His-198, respectively. The NMR data were compared with the X-ray structure of the Fab fragment of human myeloma immunoglobulin, IgG1 (lambda) New [Poljak, R. J., Amzel, L. M., Avey, H. P., Chen, B. L., Phizacherley, R. P., & Saul, F. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 3305-3310]. The NMR data are explained in terms of the crystal structure and are thus consistent with solution and crystal structure being quite similar in the constant domain of the lambda chains.