A conformational change in the Fc precludes the binding of two Fc gamma receptor molecules to one IgG

Recent NMR analyses of IgG-Fc gamma R interactions in solution have identif ied the Fc gamma R-binding site on the Fc region and provided evidence for a conformational change in the Fc occurring during the interaction. Here, K oichi Kato and colleagues discuss how this conformational change explains t he incapacity of IgG molecules to trigger responses deleterious to the orga nism, in the absence of antigen cross-linking.