Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
Proc Natl Acad Sci U S A. 2018 Feb 6;115(6):E1184-E1193. doi: 10.1073/pnas.1717495115. Epub 2018 Jan 22.
The yeast prion [PSI+] is a self-propagating amyloid of Sup35p with a folded in-register parallel β-sheet architecture. In a genetic screen for antiprion genes, using the yeast knockout collection, and , encoding nonsense-mediated mRNA decay (NMD) factors, were frequently detected. Almost all [PSI+] variants arising in the absence of Upf proteins were eliminated by restored normal levels of these proteins, and [PSI+] arises more frequently in mutants. Upf1p, complexed with Upf2p and Upf3p, is a multifunctional protein with helicase, ATP-binding, and RNA-binding activities promoting efficient translation termination and degradation of mRNAs with premature nonsense codons. We find that the curing ability of Upf proteins is uncorrelated with these previously reported functions but does depend on their interaction with Sup35p and formation of the Upf1p-Upf2p-Upf3p complex (i.e., the Upf complex). Indeed, Sup35p amyloid formation in vitro is inhibited by substoichiometric Upf1p. Inhibition of [PSI+] prion generation and propagation by Upf proteins may be due to the monomeric Upf proteins and the Upf complex competing with Sup35p amyloid fibers for available Sup35p monomers. Alternatively, the association of the Upf complex with amyloid filaments may block the addition of new monomers. Our results suggest that maintenance of normal protein-protein interactions prevents prion formation and can even reverse the process.
酵母朊病毒 [PSI+] 是 Sup35p 的一种自我传播的淀粉样蛋白，具有折叠的、在位平行的β-片层结构。在使用酵母敲除文库的抗朊病毒基因的遗传筛选中， 和 ，编码无意义介导的 mRNA 降解（NMD）因子，经常被检测到。几乎所有在没有 Upf 蛋白的情况下出现的 [PSI+] 变体都被这些蛋白的正常水平恢复所消除，并且 [PSI+] 在 突变体中更频繁地出现。Upf1p 与 Upf2p 和 Upf3p 形成复合物，是一种多功能蛋白，具有解旋酶、ATP 结合和 RNA 结合活性，促进具有过早无意义密码子的 mRNA 的有效翻译终止和降解。我们发现 Upf 蛋白的治愈能力与这些先前报道的功能无关，但确实依赖于它们与 Sup35p 的相互作用和 Upf1p-Upf2p-Upf3p 复合物（即 Upf 复合物）的形成。事实上，亚化学计量的 Upf1p 可抑制 Sup35p 淀粉样纤维的体外形成。Upf 蛋白抑制 [PSI+] 朊病毒的产生和传播可能是由于单体 Upf 蛋白和 Upf 复合物与 Sup35p 淀粉样纤维竞争可用的 Sup35p 单体。或者，Upf 复合物与淀粉样纤维的结合可能会阻止新单体的添加。我们的结果表明，维持正常的蛋白质-蛋白质相互作用可防止朊病毒的形成，甚至可以逆转这一过程。
