Site-Specific Glycosylation Analysis of Murine and Human Fcγ Receptors Reveals High Heterogeneity at Conserved N-Glycosylation Site

Abstract

Fc γ-receptors (FcγRs) on leukocytes bind immunoglobulin G (IgG) immune complexes to mediate effector functions. Dysregulation of FcγR-mediated processes contributes to multiple inflammatory diseases, including rheumatoid arthritis, lupus, and immune thrombocytopenia. Critically, immunoregulatory N-glycan modifications on both FcγRs and IgGs alter FcγR-IgG binding affinity. Rapid methods for the characterization of N-glycans across multiple Fcγ receptors are needed to propel investigations into disease-specific contributions of FcγR N-glycans. Here, we utilize nanoliquid chromatography tandem mass spectrometry (nLC-MS/MS) to characterize FcγR glycosylation and report quantitative and site-specific Nglycan characterization of recombinant human FcγRI, FcγRIIIA V158, and FcγRIIIA F158 from CHO cells and murine FcγRI, FcγRIII, and FcγRIV from NS0 cells. Data are available via ProteomeXchange with identifier PXD043966. Broad glycoform distribution (≥30) was observed at mouse FcγRIV site N159 and human FcγRIIIA site N162, an evolutionarily conserved site. Further, mouse FcγRIII N-glycopeptides spanning all four predicted N-glycosylation sequons were detected. Glycoform relative abundances for hFcγRIIIA V/F158 polymorphic variants are reported, demonstrating the clinical potential of this workflow to measure differences in glycosylation between common human FcγRIIIA allelic variants with diseaseassociated outcomes. The multi-Fcγ receptor glycoproteomic workflow reported here will empower studies focused on the role of FcγR N-glycosylation in autoimmune diseases.

Site-Specific Glycosylation Analysis of Human and Murine Fcγ Receptor II Family Members Reveals Variant-Specific N-Glycosylation

“…These glycoforms are largely consistent with our recent findings examining the site-specific N- glycosylation of human FcγRI and FcγRIII, and murine FcγRI and FcγRIV, and with site-specific glycoforms of human FcγRIIA derived from monocytes . The glycan compositions observed here on recombinant human FcγRII family receptors produced in NS0 cells are largely similar to glycan compositions detected on human FcγRI and FcγRIII (produced in CHO cells), and murine FcγRI and FcγRIV (produced in NS0 cells), with most glycoforms consistent with complex, fucosylated N- glycans . The results reported here are consistent with the findings of Cosgrave et al (2013), in which low levels of sialylated N-glycans consisting primarily of monosialylated species were reported based on the analysis of released N-glycans from recombinant human FcgRIIA and FcgRIIA also expressed in NS0 cells .…”