Abstract
Human Fcγ receptor III (FcγRIII) consists of two isoforms that are encoded by two individual genes: transmembrane FcγRIIIa and glycosylphosphatidylinositol-linked FcγRIIIb. Both isoforms can exist as a soluble form (sFcγRIII), which is composed of their extracellular region produced by proteolytic cleavage. FcγRIII-mediated immunological functions such as antibody-dependent cell-mediated cytotoxicity and phagocytosis critically depend on the N-glycosylation of FcγRIII molecules. In our previous study, high-performance liquid chromatography-based profiling indicated that N-linked oligosaccharides released from the NA2 allele of human sFcγRIIIb expressed in baby hamster kidney cells are composed of high-mannose-type oligosaccharides and core-fucosylated complex-type oligosaccharides. Here we successfully classified the N-glycans of this glycoprotein into these two types at each of the six N-glycosylation sites by liquid chromatography (LC)-electrospray tandem mass spectrometry analysis combined with endoglycosidase treatments. Our results indicated that four sites of sFcγRIIIb, Asn38, Asn74, Asn162, and Asn169, expressed only complex-type oligosaccharides, while the remaining two sites, Asn45 and Asn64 (both are not conserved in the NA1 allele), were occupied by not only complextype oligosaccharides but also high-mannose-type oligosaccharides, which are thought to be involved in the interaction of FcγRIIIb with complement receptor type 3. Together with the previously reported site-specific N-glycosylation profiling of recombinant sFcγRIIIa, this study underlines that both sFcγRIIIa and sFcγRIIIb produced in different production vehicles express core-fucosylated complex-type oligosaccharides as the major glycoforms at Asn74 and Asn162. These finding provide insights into the design and development of therapeutic antibodies because the Asn162 N-glycan significantly contributes to immunoglobulin G binding.
Highlights
Receptors for the Fc portion of IgG (FcγRs) are a heterogeneous family of membrane-associated glycoproteins, which mediate various effector and regulatory functions such as the release of inflammatory regulator, endocytosis of the immune complex, and antibody-dependent cell-mediated cytotoxicity (ADCC) [1,2,3]
Both Fcγ receptor III (FcγRIII) isoforms can exist as a soluble form that consists of an extracellular region proteolytically cleaved from the transmembrane segment [5,6,7]
The site-specific N-glycosylation profile of FcγRIIIb has not been available, our highperformance liquid chromatography (HPLC)-based N-glycosylation profiling of human sFcγRIIIb (NA2) expressed in baby hamster kidney (BHK) cells indicated that this glycoprotein possesses 14% high-mannose-type oligosaccharides and 86% complex-type oligosaccharides [25]
Summary
Receptors for the Fc portion of IgG (FcγRs) are a heterogeneous family of membrane-associated glycoproteins, which mediate various effector and regulatory functions such as the release of inflammatory regulator, endocytosis of the immune complex, and antibody-dependent cell-mediated cytotoxicity (ADCC) [1,2,3]. The site-specific N-glycosylation profile of FcγRIIIb has not been available, our highperformance liquid chromatography (HPLC)-based N-glycosylation profiling of human sFcγRIIIb (NA2) expressed in baby hamster kidney (BHK) cells indicated that this glycoprotein possesses 14% high-mannose-type oligosaccharides and 86% complex-type oligosaccharides [25]. This prompted us to perform site-specific classification of the N-linked oligosaccharides displayed on human sFcγRIIIb into high-mannoseand complex-types using liquid chromatography (LC)-electrospray tandem mass spectrometry (MS/MS) analysis in conjunction with endoglycosidase treatments.
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