Computer localization of some Gm markers on the surface of the Fc region of human immunoglobulin G

Abstract

The surface localization of some Gm markers on the Fc fragment of IgG has been identified from previously published amino acid sequences associated with known Gm markers using the atomic coordinates described by Deisenhofer, INSIGHT software and a Digital VAX 11/785 computer, which together permit a study of the three-dimensional structure of the Fc fragment. The G1m(x)-associated amino acid residue 431, the G3m(s)- and G3m(u)-associated residue 435 and the nG4m (a)- and (b)-associated residue 309 are all localized in the interface between the CH2 and CH3 domains. Furthermore, it is postulated that the G1m(a)-associated residue 356 (Asp, Glu) influences the interface formation through an ion pair interaction to Lys 439. Finally, G3m(b) and G3m(g) are associated with the interface via residues 435 and 436. The data explain why sera from patients with rheumatoid arthritis are useful tools for the detection of some Gm markers and support the view that rheumatoid factors from these patients are internal images of microbial Fc-binding proteins.