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A protein conjugation system essential for autophagy (see comments)

机译：自噬必不可少的蛋白质偶联系统（请参阅评论）

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Autophagy is a process for the bulk degradation of proteins, in which cytoplasmic components of the cell are enclosed by double-membrane structures known as autophagosomes for delivery to lysosomes or vacuoles for degradation. This process is crucial for survival during starvation and cell differentiation. No molecules have been identified that are involved in autophagy in higher eukaryotes. We have isolated 14 autophagy-defective (apg) mutants of the yeast Saccharomyces cerevisiae and examined the autophagic process at the molecular level. We show here that a unique covalent-modification system is essential for autophagy to occur. The carboxy-terminal glycine residue of Apg12, a 186-amino-acid protein, is conjugated to a lysine at residue 149 of Apg5, a 294-amino-acid protein. Of the apg mutants, we found that apg7 and apg10 were unable to form an Apg5/Apg12 conjugate. By cloning APG7, we discovered that Apg7 is a ubiquitin-E1-like enzyme. This conjugation can be reconstituted in vitro and depends on ATP. To our knowledge, this is the first report of a protein unrelated to ubiquitin that uses a ubiquitination-like conjugation system. Furthermore, Apg5 and Apg12 have mammalian homologues, suggesting that this new modification system is conserved from yeast to mammalian cells.
机译：自噬是蛋白质大量降解的过程，其中细胞的胞质成分被称为自噬体的双膜结构包围，以递送至溶酶体或液泡中进行降解。这个过程对于饥饿和细胞分化过程中的生存至关重要。尚未发现与高等真核生物自噬有关的分子。我们已经分离出14种自酿酒酵母的自噬缺陷（apg）突变体，并在分子水平上检查了自噬过程。我们在这里表明，独特的共价修饰系统对于发生自噬至关重要。 Apg12（一种186个氨基酸的蛋白质）的羧基末端甘氨酸残基在294个氨基酸的Apg5的149残基处与赖氨酸结合。在apg突变体中，我们发现apg7和apg10无法形成Apg5 / Apg12共轭物。通过克隆APG7，我们发现Apg7是一种泛素E1样酶。这种结合可以在体外重建，并取决于ATP。据我们所知，这是与泛素无关的蛋白质的首次报道，该蛋白质使用了类似泛素化的偶联系统。此外，Apg5和Apg12具有哺乳动物同源物，表明该新的修饰系统从酵母到哺乳动物细胞都是保守的。

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