Proton nuclear magnetic resonance studies of the structure of the Fc fragment of human immunoglobulin G1: comparisons of native and recombinant proteins.

The structure of the Fc fragment of human IgG1 immunoglobulin is compared for the native and recombinant proteins. A recombinant human Fc fragment was expressed by an E. coli system [Kitai K., Kudo T., Nakamura S., Masegi T., Ichikawa Y. and Horikoshi K. (1988) Appl. Microbiol. Biotechnol. 28, 52-56]. The recombinant protein, which presumably lacks oligosaccharides, was used along with the native human Fc fragment obtained by proteolytic digestion of a myeloma IgG1 protein. 1H NMR has been employed along with circular dichroism and fluorescence spectroscopy to discuss the structure of these two types of proteins. It has been concluded that (1) the overall structure of the recombinant protein is quite similar to that of the native protein, which possesses asparagine-linked oligosaccharides, but (2) a significant difference in structure exists in the neighborhood of the glycosylation site. The difference in the effector functions for the two kinds of the Fc proteins has been briefly discussed in terms of the structural change detected by 1H NMR.