FcγRIIIa is primarily expressed on natural killer cells and promotes ADCC activity through an interaction with IgG in complex with antigens. This interaction depends upon N-glycosylation of both FcγRIIIa and IgG–Fc. N-glycans at Asn162 and Asn45 of FcγRIIIa have positive and negative effects, respectively, on its reactivity with IgG . X-ray crystallographic data indicate that the Asn162 glycan directly mediates the IgG–FcγRIIIa complex formation, primarily through interaction with the N-glycan at Asn297 of Fc, while the Asn45 glycan negatively affects IgG binding through steric hindrance . The positive carbohydrate–carbohydrate interaction between the FcγRIIIa Asn162 glycan and the Fc Asn297 glycan is sterically hindered by core fucosylation of this Fc glycan. Hence, removal of the fucose residue from the IgG–Fc N-glycan results in increased affinity for the Asn162-glycosylated FcγRIIIa glycoprotein, which dramatically improves ADCC activity. These findings demonstrate that the N-glycosylation status of FcγRs and IgG–Fc can be a crucial factor in the design and development of therapeutic antibodies.
Citation: Kawasaki N, Okumoto T, Yamaguchi Y, Takahashi N, Fridman WH, et al. (2014) Site-Specific Classification of N-Linked Oligosaccharides of the Extracellular Regions of Fcγ Receptor IIIb Expressed in Baby Hamster Kidney Cells. J Glycomics Lipidomics 4:116.