唾液酸酯酶 (SIAE) 催化去除细胞表面糖蛋白上唾液酸中的 O-乙酰基，以调节 B 细胞受体信号传导和细胞凋亡等细胞过程。 SIAE 的功能丧失突变与几种常见的自身免疫性疾病有关，包括克罗恩病、溃疡性结肠炎和关节炎。为了更好地了解该蛋白质的功能和调节，我们从三种哺乳动物同源物中确定了 SIAE 的晶体结构，包括乙酸盐结合结构。结构表明催化结构域采用 SGNH 水解酶超家族的折叠。活性位点由催化二元组组成，与之前报道的催化三元组相反。尝试确定底物结合结构仅在活性位点产生水解产物乙酸盐。完整底物的刚性对接随后进行分子动力学模拟表明，活性位点并不与底物形成特异性相互作用，而是似乎广泛特异性地接受具有不同修饰的唾液酸聚糖。基于乙酸酯键合结构，提出了催化机制。疾病突变的结构图谱显示，大多数突变位于酶的表面，只会对蛋白质折叠造成轻微破坏，这表明这些突变可能会影响与其他因子的结合。这些结果提高了我们对 SIAE 生物学的理解，并可能有助于开发自身免疫性疾病和癌症的疗法。版权所有 © 2024 作者。由爱思唯尔有限公司出版。保留所有权利。

Sialic acid esterase (SIAE) catalyzes the removal of O-acetyl groups from sialic acids found on cell surface glycoproteins to regulate cellular processes such as B cell receptor signalling and apoptosis. Loss-of-function mutations in SIAE are associated with several common autoimmune diseases including Crohn's, ulcerative colitis, and arthritis. To gain a better understanding of the function and regulation of this protein, we determined crystal structures of SIAE from three mammalian homologs, including an acetate bound structure. The structures reveal that the catalytic domain adopts the fold of the SGNH hydrolase superfamily. The active site is composed of a catalytic dyad, as opposed to the previously reported catalytic triad. Attempts to determine a substrate-bound structure yielded only the hydrolyzed product acetate in the active site. Rigid docking of complete substrates followed by molecular dynamics simulations revealed that the active site does not form specific interactions with substrates, rather it appears to be broadly specific to accept sialoglycans with diverse modifications. Based on the acetate bound structure, a catalytic mechanism is proposed. Structural mapping of disease mutations reveals that most are located on the surface of the enzyme and would only cause minor disruptions to the protein fold, suggesting that these mutations likely affect binding to other factors. These results improve our understanding of SIAE biology and may aid in the development of therapies for autoimmune diseases and cancer.Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.