Degradation of citrate synthase lacking the mitochondrial targeting sequence is inhibited in cells defective in Hsp70/Hsp40 chaperones under heat stress conditions.

IF 2.4 4区 生物学 Q3 BIOTECHNOLOGY & APPLIED MICROBIOLOGY
Mayuko Hayashi, Tomoyuki Kawarasaki, Kunio Nakatsukasa
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引用次数: 0

Abstract

Most nucleus-encoded mitochondrial precursor proteins are synthesized in the cytosol and imported into mitochondria in a post-translational manner. In recent years, the quality control mechanisms of nonimported mitochondrial proteins have been intensively studied. In a previous study, we established that in budding yeast a mutant form of citrate synthase 1 (N∆Cit1) that lacks the N-terminal mitochondrial targeting sequence, and therefore mislocalizes to the cytosol is targeted for proteasomal degradation by the SCFUcc1 ubiquitin ligase complex. Here, we show that Hsp70 and Hsp40 chaperones (Ssa1 and Ydj1 in yeast, respectively) are required for N∆Cit1 degradation under heat stress conditions. In the absence of Hsp70 function, a portion of N∆Cit1-GFP formed insoluble aggregates and cytosolic foci. However, the extent of ubiquitination of N∆Cit1 was unaffected, implying that Hsp70/Hsp40 chaperones are involved in the postubiquitination step of N∆Cit1 degradation. Intriguingly, degradation of cytosolic/peroxisomal gluconeogenic citrate synthase (Cit2), an endogenous substrate for SCFUcc1-mediated proteasomal degradation, was not highly dependent on Hsp70 even under heat stress conditions. These results suggest that mitochondrial citrate synthase is thermally vulnerable in the cytosol, where Hsp70/Hsp40 chaperones are required to facilitate its degradation.

在热胁迫条件下,缺乏线粒体靶向序列的柠檬酸合成酶在Hsp70/Hsp40伴侣缺陷细胞中的降解受到抑制。
大多数由细胞核编码的线粒体前体蛋白在细胞质中合成,并以翻译后的方式导入线粒体。近年来,人们对非导入线粒体蛋白的质量控制机制进行了深入研究。在之前的一项研究中,我们发现在芽殖酵母中,柠檬酸合成酶 1(NΔCit1)的突变体缺乏 N 端线粒体靶向序列,因此会错误地定位到细胞质中,被 SCFUcc1 泛素连接酶复合物靶向进行蛋白酶体降解。在这里,我们发现 Hsp70 和 Hsp40 合子(在酵母中分别为 Ssa1 和 Ydj1)在热胁迫条件下是 N∆Cit1 降解所必需的。在缺乏 Hsp70 功能的情况下,部分 N∆Cit1-GFP 形成不溶性聚集体和细胞膜病灶。然而,N∆Cit1 泛素化的程度却不受影响,这意味着 Hsp70/Hsp40 合子参与了 N∆Cit1 降解的泛素化后步骤。耐人寻味的是,细胞膜/过氧物酶体葡萄糖酸合成酶(Cit2)是 SCFUcc1 介导的蛋白酶体降解的内源性底物,即使在热胁迫条件下,它的降解对 Hsp70 的依赖性也不高。这些结果表明,线粒体柠檬酸合成酶在细胞质中易受热胁迫,需要Hsp70/Hsp40伴侣来促进其降解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
FEMS yeast research
FEMS yeast research 生物-生物工程与应用微生物
CiteScore
5.70
自引率
6.20%
发文量
54
审稿时长
1 months
期刊介绍: FEMS Yeast Research offers efficient publication of high-quality original Research Articles, Mini-reviews, Letters to the Editor, Perspectives and Commentaries that express current opinions. The journal will select for publication only those manuscripts deemed to be of major relevance to the field and generally will not consider articles that are largely descriptive without insights on underlying mechanism or biology. Submissions on any yeast species are welcome provided they report results within the scope outlined below and are of significance to the yeast field.
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