Ipomoeassin F binds Sec61a to inhibit protein translocation.

by Zong, Guanghui; Hu, Zhijian; O'Keefe, Sarah; Tranter, Dale; Iannotti, Michael J.; Baron, Ludivine; Hall, Belinda; Corfield, Katherine; Paatero, Anja O.; Henderson, Mark J.; Roboti, Peristera; Zhou, Jianhong; Sun, Xianwei; Govindarajan, Mugunthan; Rohde, J

Ipomoeassin F is a potent natural cytotoxin that inhibits growth of many tumor cell lines with single-digit nanomolar potency by an undefined mechanism. However, its biol. and pharmacol. properties have remained largely unexplored. Building upon our earlier achievements in total synthesis and medicinal chem., we used chem. proteomics to identify Sec61a (protein transport protein Sec61 subunit alpha isoform 1), the pore-forming subunit of the Sec61 protein translocon, as a direct binding partner of ipomoeassin F in living cells. The interaction is specific and strong enough to survive lysis conditions, enabling a biotin-analog of ipomoeassin F to pull down Sec61a from live cells, yet it is also reversible as judged by fluorescent streptavidin staining. Sec61a provides the central subunit of the ER protein translocation complex, and the binding of ipomoeassin F results in a substantial, yet selective, inhibition of protein translocation in vitro and a broad ranging inhibition of protein secretion in live cells. Lastly, the unique resistance profile demonstrated by mutant cells provides compelling evidence that Sec61a is the primary mol. target of ipomoeassin F and strongly suggests that the binding of this natural product to Sec61a is distinctive. Therefore, ipomoeassin F represents the first plant-derived, carbohydrate-based member of a novel structural class that offers new opportunities to explore Sec61a function and to further investigate its potential as a therapeutic target for drug discovery.

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