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Publication Abstract from PubMed

Antibody-dependent cellular cytotoxicity (ADCC) is an important effector function determining the clinical efficacy of therapeutic antibodies. Core fucose removal from N-glycans on the Fc portion of immunoglobulin G (IgG) improves the binding affinity for Fcgamma receptor IIIa (FcgammaRIIIa) and dramatically enhances ADCC. Our previous structural analyses revealed that Tyr-296 of IgG1-Fc plays a critical role in the interaction with FcgammaRIIIa, particularly in the enhanced FcgammaRIIIa binding of nonfucosylated IgG1. However, the importance of the Tyr-296 residue in the antibody in the interaction with various Fcgamma receptors has not yet been elucidated. To further clarify the biological importance of this residue, we established comprehensive Tyr-296 mutants as fucosylated and nonfucosylated anti-CD20 IgG1s rituximab variants and examined their binding to recombinant soluble human Fcgamma receptors: shFcgammaRI, shFcgammaRIIa, shFcgammaRIIIa, and shFcgammaRIIIb. Some of the mutations affected the binding of antibody to not only shFcgammaRIIIa but also shFcgammaRIIa and shFcgammaRIIIb, suggesting that the Tyr-296 residue in the antibody was also involved in interactions with FcgammaRIIa and FcgammaRIIIb. For FcgammaRIIIa binding, almost all Tyr-296 variants showed lower binding affinities than the wild-type antibody, irrespective of their core fucosylation, particularly in Y296K and Y296P. Notably, only the Y296W mutant showed improved binding to FcgammaRIIIa. The 3.00 A-resolution crystal structure of the nonfucosylated Y296W mutant in complex with shFcgammaRIIIa harboring two N-glycans revealed that the Tyr-to-Trp substitution increased the number of potential contact atoms in the complex, thus improving the binding of the antibody to shFcgammaRIIIa. The nonfucosylated Y296W mutant retained high ADCC activity, relative to the nonfucosylated wild-type IgG1, and showed greater binding affinity for FcgammaRIIa. Our data may improve our understanding of the biological importance of human IgG1-Fc Tyr-296 in interactions with various Fcgamma receptors, and have applications in the modulation of the IgG1-Fc function of therapeutic antibodies.

Importance of the Side Chain at Position 296 of Antibody Fc in Interactions with FcgammaRIIIa and Other Fcgamma Receptors.,Isoda Y, Yagi H, Satoh T, Shibata-Koyama M, Masuda K, Satoh M, Kato K, Iida S PLoS One. 2015 Oct 7;10(10):e0140120. doi: 10.1371/journal.pone.0140120., eCollection 2015. PMID:26444434^[7]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.