HDX-MS and MD Simulations Provide Evidence for Stabilization of the IgG1-FcγRIa (CD64a) Immune Complex Through Intermolecular Glycoprotein Bonds

Previous reports present different models for the stabilization of the Fc-Fc gamma RI immune complex. Although accord exists on the importance of L235 in IgG1 and some hydrophobic contacts for complex stabilization, discord exists regarding the existence of stabilizing glycoprotein contacts between glycans of IgG1 and a conserved FG-loop ((171)MGKHRY(176)) of Fc gamma RIa. Complexes formed from the Fc gamma RIa receptor and IgG1s containing biantennary glycans with N-acetylglucosamine, galactose, and alpha 2,6-N-acetylneuraminic terminations were measured by hydrogen-deuterium exchange mass spectrometry (HDX-MS), classified for dissimilarity with Welch's ANOVA and Games-Howell post hoc procedures, and modeled with molecular dynamics (MD) simulations. For each glycoform of the IgG1-Fc gamma RIa complex peptic peptides of Fab, Fc and Fc gamma RIa report distinct H/D exchange rates. MD simulations corroborate the differences in the peptide deuterium content through calculation of the percent of time that transient glycan-peptide bonds exist. These results indicate that stability of IgG1-Fc gamma RIa complexes correlate with the presence of intermolecular glycoprotein interactions between the IgG1 glycans and the (KHR175)-K-173 motif within the FG-loop of Fc gamma RIa. The results also indicate that intramolecular glycanprotein bonds stabilize the Fc region in isolated and complexed IgG1. Moreover, HDX-MS data evince that the Fab domain has glycan-protein binding contacts within the IgG1-Fc gamma RI complex. Published by Elsevier Ltd.

Automated summary

Previous studies have proposed different models for stabilizing the Fc-Fc gamma RI immune complex. This study used multiple experimental methods to investigate the role of glycoprotein interactions between IgG1 glycans and the FG-loop of Fc gamma RIa in complex stabilization. The results showed that both intermolecular and intramolecular glycoprotein bonds contribute to the stability of the complex.