The Fc portion of immunoglobulin G (IgG) promotes defensive effector functions in the immune system by interacting with Fcγ receptors and complement component C1q. These interactions critically depend on N-glycosylation at Asn297 of each C_H2 domain, where biantennary complex-type oligosaccharides contain microheterogeneities resulting primarily from the presence or absence of non-reducing terminal galactose residues. Crystal structures of Fc have shown that a pair of N-glycans is located between the two C_H2 domains. Here we applied our metabolic isotope labeling technique using mammalian cells for in-solution structural characterization of mouse IgG2b-Fc glycoforms with a molecular mass of 54 kDa. Based on spectral assignments of the N-glycans as well as polypeptide backbones of Fc, we probed conformational perturbations of Fc induced by N-glycan trimming, especially enzymatic degalactosylation. The results indicated that degalactosylation structurally perturbed the Fc region through rearrangement of glycan-protein interactions. The spectral assignments of IgG2b-Fc glycoprotein will provide the basis for NMR investigation of its dynamic conformations and interactions with effector molecules in solution.

免疫球蛋白 G (IgG) 的 Fc 部分通过与 Fcγ 受体和补体成分 C1q 相互作用，促进免疫系统中的防御效应功能。这些相互作用主要取决于每个_CH 2结构域的Asn297处的N-糖基化，其中双触角复合型寡糖含有主要由非还原性末端半乳糖残基的存在或不存在引起的微异质性。 Fc的晶体结构表明一对N-聚糖位于两个_CH 2 结构域之间。在这里，我们应用代谢同位素标记技术，使用哺乳动物细胞对分子量为 54 kDa 的小鼠 IgG2b-Fc 糖型进行溶液内结构表征。基于N-聚糖以及Fc的多肽主链的光谱分配，我们探测了由N-聚糖修剪，特别是酶促脱半乳糖基化诱导的Fc构象扰动。结果表明，脱半乳糖基化通过聚糖-蛋白质相互作用的重排在结构上扰乱 Fc 区。 IgG2b-Fc 糖蛋白的光谱分配将为 NMR 研究其动态构象以及与溶液中效应分子的相互作用提供基础。