Unique carbohydrate–carbohydrate interactions are required for high affinity binding between FcγRIII and antibodies lacking core fucose

Abstract

Antibody-mediated cellular cytotoxicity (ADCC), a key immune effector mechanism, relies on the binding of antigen-antibody complexes to Fcγ receptors expressed on immune cells. Antibodies lacking core fucosylation show a large increase in affinity for FcγRIIIa leading to an improved receptor-mediated effector function. Although afucosylated IgGs exist naturally, a next generation of recombinant therapeutic, glycoenginereed antibodies is currently being developed to exploit this finding. In this study, the crystal structures of a glycosylated Fcγ receptor complexed with either afucosylated or fucosylated Fc were determined allowing a detailed, molecular understanding of the regulatory role of Fc-oligosaccharide core fucosylation in improving ADCC. The structures reveal a unique type of interface consisting of carbohydratecarbohydrate interactions between glycans of the receptor and the afucosylated Fc. In contrast, in the complex structure with fucosylated Fc, these contacts are weakened or nonexistent, explaining the decreased affinity for the receptor. These findings allow us to understand the higher efficacy of therapeutic antibodies lacking the core fucose and also suggest a unique mechanism by which the immune system can regulate antibody-mediated effector functions.immunoglobulin | afucosylation | antibody effector function | X-ray crystallography

Rapid screening of IgG quality attributes – effects on Fc receptor binding

“…Furthermore, fucosylation levels of the antibody have an impact on the binding to FcγRIIIa and FcγRIIIb, whereas no differences in binding were measured on any of the other Fc receptors. These results are in agreement with the literature 13, 16, 17, 18, 19. None of the cited references studied the effect of DG on fraction bound at neutral pH, and we have demonstrated that there is a significant impact.…”

Molecular modeling of antibodies for the treatment of TNFα‐related immunological diseases

“…2011), and the complete structure of a murine immunoglobulin (1IGT) used either as a protein template (Harris et al. 1997) to drive the 3D modeling or to extract its Fc portion for building one of our chimera models.…”

“…2011). Furthermore, we noticed that Chimera 1A and Chimera 1B share very similar features from a structural point of view after their energy minimization (the static rmsd between the two chimera backbones was about 2 Å with both glycosylation ladders alternatively retained from 1IGT or 3SGJ), whereas the main differences were observed in their comparison with Chimera 2 .…”

“…Finally, we aligned the sequence of the human IgG–Fc glycoform (3SGJ or 3SGK) (Ferrara et al. 2011) with the Fc portion of the murine Ig (1IGT.pdb) (Harris et al. 1997).…”

The “less-is-more” in therapeutic antibodies: Afucosylated anti-cancer antibodies with enhanced antibody-dependent cellular cytotoxicity

“…showed that a unique kind of carbohydrate–carbohydrate interaction coupled with increased number of newly formed hydrogen bonds and van der Waals contacts likely contribute to the increased binding affinity observed between afucosylated Fc and the Asn162-glycosylated receptor 64 . However, in the crystal structure of fucosylated Fc in complex with FcγRIIIa, the core fucose is oriented toward the second GlcNAc of the N -glycan attached to Asn162 and has to accommodate in the interface between the interacting glycan chains 64 . As a result, the whole oligosaccharide unit on Asn162 moves away from the Fc glycan, which leads to a weakened FcγRIIIa-IgG interaction.…”