13C NMR study of the mode of interaction in solution of the B fragment of staphylococcal protein A and the Fc fragments of mouse immunoglobulin G.

The mode of interaction of the B domain (FB) of staphylococcal protein A and the Fc fragments of mouse immunoglobulin G (IgG) has been investigated by 13C NMR spectroscopy. Mouse IgG1, IgG2a, and IgG2b proteins have been selectively labeled with 13C at the carbonyl carbon of His, Met, Trp or Tyr residue and used to prepare the corresponding Fc fragments by limited proteolysis. Site-specific resonance assignments have been made for each of these Fc analogues. FB was reported to form two contacts (contact 1 and contact 2) with human Fc in the crystal [Biochemistry 20 (1981) 2361-2370]. Comparisons of the chemical shift data of the Fc fragments observed in the absence and presence of FB have led us to conclude that in solution contact 1 is responsible for the formation of the Fc-FB complexes.