The IgG-specific endoglycosidases EndoS and EndoS2 from can remove conserved -linked glycans present on the Fc region of host antibodies to inhibit Fc-mediated effector functions. These enzymes are therefore being investigated as therapeutics for suppressing unwanted immune activation, and have additional application as tools for antibody glycan remodeling. EndoS and EndoS2 differ in Fc glycan substrate specificity due to structural differences within their catalytic glycosyl hydrolase domains. However, a chimeric EndoS enzyme with a substituted glycosyl hydrolase from EndoS2 loses catalytic activity, despite high structural homology between the two enzymes, indicating either mechanistic divergence of EndoS and EndoS2, or improperly-formed domain interfaces in the chimeric enzyme. Here, we present the crystal structure of the EndoS2-IgG1 Fc complex determined to 3.0 Å resolution. Comparison of complexed and unliganded EndoS2 reveals relative reorientation of the glycosyl hydrolase, leucine-rich repeat and hybrid immunoglobulin domains. The conformation of the complexed EndoS2 enzyme is also different when compared to the earlier EndoS-IgG1 Fc complex, and results in distinct contact surfaces between the two enzymes and their Fc substrate. These findings indicate mechanistic divergence of EndoS2 and EndoS. It will be important to consider these differences in the design of IgG-specific enzymes, developed to enable customizable antibody glycosylation.

中文翻译：

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IgG 特异性糖苷内切酶 EndoS 和 EndoS2 通过构象和抗​​体识别来区分

IgG特异性内切糖苷酶EndoS和EndoS2可以去除宿主抗体Fc区上存在的保守连接聚糖，以抑制Fc介导的效应子功能。因此，这些酶正在被研究作为抑制不需要的免疫激活的治疗剂，并且具有作为抗体聚糖重塑工具的额外应用。 EndoS 和 EndoS2 由于其催化糖基水解酶结构域内的结构差异而在 Fc 聚糖底物特异性方面存在差异。然而，尽管两种酶之间具有高度的结构同源性，但带有来自 EndoS2 的糖基水解酶取代的嵌合 EndoS 酶却失去了催化活性，这表明 EndoS 和 EndoS2 的机制存在差异，或者嵌合酶中结构域界面的形成不正确。在这里，我们展示了以 3.0 Å 分辨率测定的 EndoS2-IgG1 Fc 复合物的晶体结构。复合的和未配体的 EndoS2 的比较揭示了糖基水解酶、富含亮氨酸的重复序列和杂合免疫球蛋白结构域的相对重新定向。与早期的 EndoS-IgG1 Fc 复合物相比，复合的 EndoS2 酶的构象也有所不同，并导致两种酶及其 Fc 底物​​之间形成不同的接触表面。这些发现表明 EndoS2 和 EndoS 的机制存在差异。在 IgG 特异性酶的设计中考虑这些差异非常重要，这些酶的开发是为了实现可定制的抗体糖基化。