Deciphering N-Glycosylation Dynamics of Serum Monoclonal Immunoglobulins in Multiple Myeloma via EThcD-sceHCD-MS/MS

Serum glycoprotein glycosylation changes can indicate disease onset and progression. However, the site-specific N-glycosylation of monoclonal immunoglobulins (M-proteins) in multiple myeloma (MM) and its clinical implications are unclear. In this study, we isolated pathogenic micromonoclonal IgA or IgG (approximately 2 μg) from IgA-MM patients (<i>n</i> = 22) and IgG-MM patients (<i>n</i> = 30), and normal polyclonal IgA and IgG from healthy controls (HCs) (<i>n</i> = 16). Using EThcD-sceHCD-MS/MS, the N-glycosylation dynamics of serum M-proteins in MM were determined. Compared with polyclonal IgA1 from HCs, monoclonal IgA1 from IgA-MM patients had higher fucosylation (58.1% vs 32.1%, <i>p</i> < 0.001), sialylation (68.0% vs 50.8%, <i>p</i> = 0.011), and mannosylation (1.5% vs 0.3%, <i>p</i> < 0.001). While, monoclonal IgG1 from IgG-MM patients had higher fucosylation (97.8% vs 95.3%, <i>p</i> < 0.001). In addition, specific N-glycan abundances correlated with MM clinical features: for IgA1, HexNAc5Hex5Fuc1NeuAc1 was associated with hypocomplementemia; for IgG1, HexNAc4Hex3Fuc1 was associated with the serum albumin level (<i>r</i> = -0.363, <i>p</i> = 0.049) and estimated glomerular filtration rate (<i>r</i> = -0.433, <i>p</i> = 0.017); and HexNAc4Hex5 was associated with therapeutic prognosis. In conclusion, monoclonal IgA1 and IgG1 in MM patients and their polyclonal isotypes in HCs have distinct N-glycosylation profiles, and specific N-glycans of M-proteins are associated with MM characteristics and therapeutic prognosis.