Structural basis for improved efficacy of therapeutic antibodies on defucosylation of their Fc glycans

Removal of the fucose residue from the N-glycans of the Fc portion of immunoglobulin G (IgG) results in a dramatic enhancement of antibody-dependent cellular cytotoxicity (ADCC) through improved affinity for Fc gamma receptor IIIa (Fc gamma RIIIa). Here, we present the 2.2-angstrom structure of the complex formed between nonfucosylated IgG1-Fc and a soluble form of Fc gamma RIIIa (sFc gamma RIIIa) with two N-glycosylation sites. The crystal structure shows that one of the two N-glycans of sFc gamma RIIIa mediates the interaction with nonfucosylated Fc, thereby stabilizing the complex. However, fucosylation of the Fc N-glycans inhibits this interaction, because of steric hindrance, and furthermore, negatively affects the dynamics of the receptor binding site. Our results offer a structural basis for improvement in ADCC of therapeutic antibodies by defucosylation.