Department of Medical Biochemistry and Cell Biology, University of Gothenburg, 405 30 Gothenburg, Sweden.
Swedish NMR Centre, University of Gothenburg, 405 30 Gothenburg, Sweden.
Cell Rep. 2024 May 28;43(5):114207. doi: 10.1016/j.celrep.2024.114207. Epub 2024 May 9.
The MUC2 mucin protects the colonic epithelium by a two-layered mucus with an inner attached bacteria-free layer and an outer layer harboring commensal bacteria. CysD domains are 100 amino-acid-long sequences containing 10 cysteines that separate highly O-glycosylated proline, threonine, serine (PTS) regions in mucins. The structure of the second CysD, CysD2, of MUC2 is now solved by nuclear magnetic resonance. CysD2 shows a stable stalk region predicted to be partly covered by adjacent O-glycans attached to neighboring PTS sequences, whereas the CysD2 tip with three flexible loops is suggested to be well exposed. It shows transient dimer interactions at acidic pH, weakened at physiological pH. This transient interaction can be stabilized in vitro and in vivo by transglutaminase 3-catalyzed isopeptide bonds, preferring a specific glutamine residue on one flexible loop. This covalent dimer is modeled suggesting that CysD domains act as connecting hubs for covalent stabilization of mucins to form a protective mucus.
黏蛋白 MUC2 通过双层黏液保护结肠上皮细胞，内层黏附无菌层，外层含有共生菌。CysD 结构域是由 100 个氨基酸组成的序列，包含 10 个半胱氨酸，将黏蛋白中的高度 O-糖基化脯氨酸、苏氨酸、丝氨酸（PTS）区域分隔开。MUC2 的第二个 CysD（CysD2）的结构现已通过核磁共振解决。CysD2 显示出稳定的茎干区域，预测部分被附着在邻近 PTS 序列上的相邻 O-聚糖覆盖，而带有三个灵活环的 CysD2 尖端则被认为暴露良好。它在酸性 pH 下显示出瞬时二聚体相互作用，在生理 pH 下减弱。这种瞬时相互作用可以在体外和体内通过转谷氨酰胺酶 3 催化的异肽键稳定，偏爱一个灵活环上的特定谷氨酰胺残基。该共价二聚体的模型表明，CysD 结构域作为黏蛋白的共价稳定的连接枢纽，形成保护性黏液。
