The hormone melatonin, secreted from the pineal gland, mediates multiple physiological effects including modulation of Wnt/β‐catenin signalling. The Wnt palmitoleate lipid modification is essential for its signalling activity, while the carboxylesterase Notum can remove the lipid from Wnt and inactivate it. Notum enzyme inhibition can therefore upregulate Wnt signalling. While searching for Notum inhibitors by crystallographic fragment screening, a hit compound N‐[2‐(5‐fluoro‐1H‐indol‐3‐yl)ethyl]acetamide that is structurally similar to melatonin came to our attention. We then soaked melatonin and its precursor N‐acetylserotonin into Notum crystals and obtained high‐resolution structures (≤1.5 Å) of their complexes. In each of the structures, two compound molecules bind with Notum: one at the enzyme's catalytic pocket, overlapping the space occupied by the acyl tail of the Wnt palmitoleate lipid, and the other at the edge of the pocket opposite the substrate entrance. Although the inhibitory activity of melatonin shown by in vitro enzyme assays is low (IC₅₀ 75 µmol/L), the structural information reported here provides a basis for the design of potent and brain accessible drugs for neurodegenerative diseases such as Alzheimer's disease, in which upregulation of Wnt signalling may be beneficial.

中文翻译：

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褪黑激素作为 Wnt 脱酰酶 Notum 抑制剂的结构表征


松果体分泌的褪黑激素可介导多种生理效应，包括调节 Wnt/β-连环蛋白信号传导。 Wnt 棕榈油酸酯脂质修饰对其信号活性至关重要，而羧酸酯酶 Notum 可以去除 Wnt 上的脂质并使其失活。因此，Notum 酶抑制可以上调 Wnt 信号传导。在通过晶体片段筛选寻找 Notum 抑制剂时，一种与褪黑激素结构相似的热门化合物 N-[2-(5-氟-1H-吲哚-3-基)乙基]乙酰胺引起了我们的注意。然后，我们将褪黑激素及其前体 N-乙酰血清素浸泡到 Notum 晶体中，并获得了它们复合物的高分辨率结构（≤1.5 Å）。在每个结构中，两个化合物分子与 Notum 结合：一个位于酶的催化口袋，与 Wnt 棕榈油酸酯脂质的酰基尾部占据的空间重叠，另一个位于与底物入口相对的口袋边缘。尽管体外酶测定显示褪黑激素的抑制活性较低（IC ₅₀ 75 µmol/L），但本文报道的结构信息为设计针对阿尔茨海默病等神经退行性疾病的有效且脑可及的药物提供了基础，其中Wnt 信号传导的上调可能是有益的。