13C-NMR spectral analysis of the structures of mouse immunoglobulin G1 carrying allotypes a and j.

A novel 13C nuclear magnetic resonance (NMR) method is described for the detection of subtle structural differences between mouse immunoglobulins carrying different allotypes. Fc fragments of mouse IgG1 antibodies carrying allotypes a and j have been selectively labeled with [1-13C]methionine. 13C-NMR spectra have shown that the microenvironment around Met-398 is significantly different for the two kinds of allotypes. Peptide mapping and amino acid sequence analyses have revealed that Val-406 of IgG1 carrying allotype a is substituted for Ile in the case of allotype j. X-ray crystallographic data indicate that Met-398 is in close spatial proximity to Val (Ile)-406. We therefore conclude that the 13C-NMR method can provide us with a novel spectroscopic probe for the structural characterization of allotypic markers.