Faculty and Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya, 467-8603, Japan.
Department of Medical Life Science, Graduate School of Medical Life Science, Yokohama City University, Suehiro-cho 1-7-29, Tsurumi-ku, Yokohama, 230-0045, Japan.
Sci Rep. 2018 Feb 9;8(1):2719. doi: 10.1038/s41598-018-21145-y.
Fc-receptors for immunoglobulin G (FcγRs) mediate a variety of effector and regulatory mechanisms in the immune system. N-glycosylation of FcγRs critically affects their functions which is well exemplified by antibody-dependent cell-mediated cytotoxicity (ADCC) and phagocytosis mediated by homologous FcγRIIIa and FcγRIIIb, respectively. Although several reports describe N-glycosylation profiles of recombinant FcγRIII glycoproteins, much remains unknown regarding their native glycoforms. Here we performed site-specific N-glycosylation profiling of a soluble form of FcγRIIIb purified from human serum based on mass spectrometric analysis. Our data indicate a distinct and common tendency of the glycoforms exhibited at each N-glycosylation site between the native and the previously reported recombinant FcγRIII glycoproteins. Among the six N-glycosylation sites of serum soluble FcγRIIIb, Asn45 was shown to be exclusively occupied by high-mannose-type oligosaccharides, whereas the remaining sites were solely modified by the complex-type oligosaccharides with sialic acid and fucose residues. The results of our endogenous FcγRIII glycoform analyses are important for the optimization of therapeutic antibody efficacy.
Fc 受体（FcγRs）介导了免疫系统中的多种效应和调节机制。FcγRs 的 N 糖基化对其功能至关重要，这在同源 FcγRIIIa 和 FcγRIIIb 介导的抗体依赖性细胞介导的细胞毒性（ADCC）和吞噬作用中得到了很好的例证。尽管有几份报告描述了重组 FcγRIII 糖蛋白的 N 糖基化谱，但对于其天然糖型仍知之甚少。在这里，我们基于质谱分析，对从人血清中纯化的可溶性 FcγRIIIb 进行了位点特异性 N 糖基化分析。我们的数据表明，在天然和先前报道的重组 FcγRIII 糖蛋白中，每个 N 糖基化位点的糖型表现出明显而共同的趋势。在血清可溶性 FcγRIIIb 的六个 N 糖基化位点中，Asn45 被证明仅被高甘露糖型寡糖占据，而其余位点仅被带有唾液酸和岩藻糖残基的复杂型寡糖修饰。我们对内源性 FcγRIII 糖型分析的结果对于优化治疗性抗体的疗效非常重要。
