Department of Immunology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, 100005 Beijing, China.
Glycobiology. 2010 Jul;20(7):905-15. doi: 10.1093/glycob/cwq048. Epub 2010 Apr 8.
FcalphaR (CD89) is the Fc receptor for immunoglobulin A (IgA) and plays important roles in IgA-mediated immune responses. It is a heavily glycosylated protein with six potential N-linked glycosylation sites. Previous reports showed that abnormal glycosylation of FcalphaR was involved in some diseases, including human immunodeficiency virus infection, alcoholic liver cirrhosis and IgA nephropathy. In this study, we examined the effects of N-glycosylation on interaction between FcalphaR and IgA. We found that depletion of N-glycosylation of FcalphaR transfected in Chinese hamster ovary (CHO) cells by tunicamycin resulted in increased IgA binding. To identify which glycosylation site is responsible for increased IgA binding, we performed site-directed mutagenesis at each N-linked glycosylation site by changing asparagine to glutamine. Flow cytometry analysis of IgA binding to CHO cells transfected with mutated FcalphaR showed that deglycosylation of FcalphaR at individual N44, N120, N156, N165 or N177 site did not affect IgA binding but deglycosylation at N58 resulted in marked increase of IgA binding. Similar result was shown for N58Q-FcalphaR transfected RBL2H3, a rat basophilic leukemia cell line. Furthermore, increased IgA binding was also observed on desialylated FcalphaR after neuraminidase treatment and desialylation of N58 contributed most to the increased IgA binding. These data demonstrated that glycosylation at N58 site influenced FcalphaR binding to IgA.
FcαR（CD89）是免疫球蛋白 A（IgA）的 Fc 受体，在 IgA 介导的免疫反应中发挥重要作用。它是一种高度糖基化的蛋白质，有六个潜在的 N 连接糖基化位点。先前的报告表明，FcαR 的异常糖基化与一些疾病有关，包括人类免疫缺陷病毒感染、酒精性肝硬化和 IgA 肾病。在这项研究中，我们研究了 N-糖基化对 FcαR 与 IgA 相互作用的影响。我们发现，衣霉素耗尽中国仓鼠卵巢（CHO）细胞中转染的 FcαR 的 N-糖基化导致 IgA 结合增加。为了确定哪个糖基化位点负责增加的 IgA 结合，我们通过将天冬酰胺突变为谷氨酰胺，在每个 N-连接糖基化位点进行定点突变。流式细胞术分析转染突变 FcαR 的 CHO 细胞中 IgA 的结合表明，单个 N44、N120、N156、N165 或 N177 位点的 FcαR 去糖基化并不影响 IgA 结合，但 N58 位点的去糖基化导致 IgA 结合显著增加。在转染 RBL2H3（大鼠嗜碱性白血病细胞系）的 N58Q-FcαR 中也观察到类似的结果。此外，神经氨酸酶处理后去唾液酸化的 FcαR 也观察到 IgA 结合增加，并且 N58 的去唾液酸化对增加的 IgA 结合贡献最大。这些数据表明，N58 位点的糖基化影响 FcαR 与 IgA 的结合。
