Immunoglobulin A Carries SulfatedN-glycans Primarily at the Tailpiece Site – An Oxonium-Ion-Guided Approach for Site-SpecificN-glycan Identification

Abstract

SulfatedN-glycans from human immunoglobulin A (IgA) were recently discovered via glycomic approaches. However, their site-specific description is still pending. CertainN-glycan structures at specificN-glycosylation sites in IgA are crucial for microbial neutralization and effector functions. For instance, sialylatedN-glycans on the C-terminal tailpiece mediate anti-viral activity by interfering with sialic-acid-binding viruses. SulfatedN-glycan epitopes can be ligands for viral proteins and thus play a role in the immune response. In this study, we performed a site-specific screening for sulfatedN-glycans in two commercially available human serum IgA samples employing an in-depthN-glycoproteomic approach, previously developed by us. We found evidence of complex-type and hybrid-typeN-glycans containing sulfatedN-acetylhexosamine (sulfated HexNAc) attached to theN-glycosylation sites in the tailpiece and the CH2 domain of both IgA subclasses. A detailed comparison of theN-glycosylation profiles of human serum IgA samples from two suppliers showed suchN-glycans with sulfated HexNAc consistently in higher abundance in the tailpiece region. Surprisingly, also complex-typeN-glycan compositions bearingO-acetylated sialic acid were identified in the tailpiece. These findings have not been described before for a site-specific glycopeptide analysis. Overall, our work provides a methodology for performing a dedicated site-specific search for sulfated andO-acetylatedN-glycans that can be easily transferred, e.g. to human IgA derived from mucosal tissues, milk, or saliva. Our future aim is to include sulfatedN-glycans into longitudinal studies of IgAN-glycosylation and to investigate their role as a biomarker and a treatment option.Abstract Figure