- 第3日 6月24日（金） P会場（501，502，503）
The interaction between immunoglobulin G1 (IgG1) and Fc gamma receptor IIIa (FcγRIIIa) is essential for mediating immune responses. IgG1 is composed of two Fab portions and one Fc portion. FcγRIIIa is expressed primarily on natural killer cells and consists of two extracellular domains: the membrane-distal domain (D1) and membrane-proximal domain (D2). Recent studies have shown that Fab and Fc are involved in IgG-FcγRIII interactions. Here, we conducted hydrogen/deuterium exchange mass spectrometry (HDX-MS) and crosslinking mass spectrometry (XL-MS) to clarify the interaction sites and structural changes upon formation of IgG-FcγRIII complexes using marketed therapeutic antibodies. Moreover, the influence of antigen-binding on IgG-FcγRIII interactions was investigated by HDX-MS. Combined HDX-MS and XL-MS revealed that the CL domain of Fab was in close proximity to FcγRIIIa, indicating that this domain specifically interacts with D1 and D2 of FcγRIIIa. The decreases in deuterium uptake of the segments in the CH1 may represent another interacting region with FcγRIIIa. Moreover, our HDX-MS detected the structural alterations in CH3 caused by FcγRIIIa-binding and the structural alterations in Fab caused by antigen-binding, which potentially facilitate the stabilization and clusterization of antigen-IgG-FcγRIII complexes for the subsequent activation of immune cells.