Institute of Biotechnology, University of Helsinki, Viikinkaari 1, Biocenter 3, Helsinki 00014, Finland.
Department of Pharmaceutical Chemistry, Institute for Neurodegenerative Disease, University of California at San Francisco, San Francisco, CA 94038, USA.
Cell Chem Biol. 2016 May 19;23(5):561-566. doi: 10.1016/j.chembiol.2016.04.008.
Apratoxin A is a cytotoxic natural product that prevents the biogenesis of secretory and membrane proteins. Biochemically, apratoxin A inhibits cotranslational translocation into the ER, but its cellular target and mechanism of action have remained controversial. Here, we demonstrate that apratoxin A prevents protein translocation by directly targeting Sec61α, the central subunit of the protein translocation channel. Mutagenesis and competitive photo-crosslinking studies indicate that apratoxin A binds to the Sec61 lateral gate in a manner that differs from cotransin, a substrate-selective Sec61 inhibitor. In contrast to cotransin, apratoxin A does not exhibit a substrate-selective inhibitory mechanism, but blocks ER translocation of all tested Sec61 clients with similar potency. Our results suggest that multiple structurally unrelated natural products have evolved to target overlapping but non-identical binding sites on Sec61, thereby producing distinct biological outcomes.
阿普拉毒素 A 是一种细胞毒性天然产物，可阻止分泌蛋白和膜蛋白的生物发生。从生化角度来看，阿普拉毒素 A 抑制共翻译易位到内质网，但它的细胞靶标和作用机制一直存在争议。在这里，我们证明阿普拉毒素 A 通过直接靶向蛋白易位通道的中心亚基 Sec61α 来阻止蛋白易位。诱变和竞争性光交联研究表明，阿普拉毒素 A 以不同于 cotransin（一种底物选择性 Sec61 抑制剂）的方式结合 Sec61 侧门。与 cotransin 不同，阿普拉毒素 A 不表现出底物选择性抑制机制，而是以相似的效力阻断所有测试的 Sec61 客户的 ER 易位。我们的结果表明，多种结构上不相关的天然产物已经进化到针对 Sec61 上重叠但不相同的结合位点，从而产生不同的生物学结果。
