Protein glycosylation is a crucial mediator of biological functions and is tightly regulated in health and disease. However, interrogating complex protein glycoforms is challenging, as current lectin tools are limited by cross-reactivity while mass spectrometry typically requires biochemical purification and isolation of the target protein. Here, we describe a method to identify and characterize a class of nanobodies that can distinguish glycoforms without reactivity to off-target glycoproteins or glycans. We apply this technology to immunoglobulin G (IgG) Fc glycoforms and define nanobodies that specifically recognize either IgG lacking its core-fucose or IgG bearing terminal sialic acid residues. By adapting these tools to standard biochemical methods, we can clinically stratify dengue virus and SARS-CoV-2 infected individuals based on their IgG glycan profile, selectively disrupt IgG–Fcγ receptor binding both in vitro and in vivo, and interrogate the B cell receptor (BCR) glycan structure on living cells. Ultimately, we provide a strategy for the development of reagents to identify and manipulate IgG Fc glycoforms.

中文翻译：

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合成纳米抗体作为区分 IgG Fc 糖型的工具

蛋白质糖基化是生物功能的重要介质，在健康和疾病中受到严格调控。然而，询问复杂的蛋白质糖型具有挑战性，因为目前的凝集素工具受到交叉反应的限制，而质谱法通常需要目标蛋白质的生化纯化和分离。在这里，我们描述了一种识别和表征一类纳米抗体的方法，这些纳米抗体可以区分糖型而不会对脱靶糖蛋白或聚糖产生反应。我们将这项技术应用于免疫球蛋白 G (IgG) Fc 糖型，并定义了特异性识别缺乏核心岩藻糖的 IgG 或带有末端唾液酸残基的 IgG 的纳米抗体。通过使这些工具适应标准生化方法，我们可以根据感染者的 IgG 聚糖谱对登革热病毒和 SARS-CoV-2 感染者进行临床分层，在体外和体内选择性地破坏 IgG-Fcγ 受体结合，并研究活细胞上的 B 细胞受体 (BCR) 聚糖结构。最终，我们提供了一种用于开发试剂以识别和操作 IgG Fc 糖型的策略。