12] Reductive methylation and carbon-13 nuclear magnetic resonance in structure—function studies of Fc fragment and its subfragments

Abstract

This chapter focuses on the structure–function properties of the Fc fragment and subfragments. The specific subfragments discussed in the chapter are the CH2 fragment; residues 225–338 of chain A and residues 225–248 of chain B; pFc' residues 333–443; and tFc' residues 339 (or 341)–443. The Fc region of immunoglobulin G (IgG), made up of the disulfide linkage and the CH2 and CH3 domains of both heavy chains, mediates many of the biological functions of the humoral immune response, including complement fixation, antibody-dependent cytotoxicity, 1–2 IgG binding to macrophages, and the release of histamine from mast cells. The comparisons between the Fc fragment and its subfragments allow to assess the detailed similarities (and hence conservation of structure) between the larger fragment and the singie-domain fragments and to conclude that while the structure of the CH3 domain is very well conserved in the pFc' and tFc' subfragrnents, the structural conservation in the CH2 domain is much weaker. An important finding related to the CH2 domain is the association of the single-residue resonances 2, 6, and 8 with the CH2 domain; they provide single-lysine probes of events in the CH2 domain that may be used to monitor their interactions in the Fc fragment.