2019•Scientific ReportsOpen access
The Fab portion of immunoglobulin G contributes to its binding to Fcγ receptor III
Rina Yogo, Yuki Yamaguchi, Hiroki Watanabe, Hirokazu Yagi, Tadashi Satoh, Mahito Nakanishi, Masayoshi Onitsuka, Takeshi Ōmasa, Mari Shimada, Takahiro Maruno, Tetsuo Torisu, Shio Watanabe, Daisuke Higo, Takayuki Uchihashi, Saeko Yanaka, Susumu Uchiyama, Koichi Kato
Abstract
Most cells active in the immune system express receptors for antibodies which mediate a variety of defensive mechanisms. These receptors interact with the Fc portion of the antibody and are therefore collectively called Fc receptors. Here, using high-speed atomic force microscopy, we observe interactions of human, humanized, and mouse/human-chimeric immunoglobulin G1 (IgG1) antibodies and their cognate Fc receptor, FcγRIIIa. Our results demonstrate that not only Fc but also Fab positively contributes to the interaction with the receptor. Furthermore, hydrogen/deuterium exchange mass spectrometric analysis reveals that the Fab portion of IgG1 is directly involved in its interaction with FcγRIIIa, in addition to the canonical Fc-mediated interaction. By targeting the previously unidentified receptor-interaction sites in IgG-Fab, our findings could inspire therapeutic antibody engineering.