Mizushima N, Noda T, Yoshimori T, Tanaka Y, Ishii T, George M D, Klionsky D J, Ohsumi M, Ohsumi Y
Department of Cell Biology, National Institute for Basic Biology, Okazaki, Japan.
Nature. 1998 Sep 24;395(6700):395-8. doi: 10.1038/26506.
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.
自噬是一种蛋白质大量降解的过程，在此过程中，细胞的细胞质成分被称为自噬体的双膜结构所包裹，以便输送到溶酶体或液泡中进行降解。这一过程对于饥饿期间的生存和细胞分化至关重要。在高等真核生物中尚未鉴定出参与自噬的分子。我们分离出了酿酒酵母的14个自噬缺陷（apg）突变体，并在分子水平上研究了自噬过程。我们在此表明，一种独特的共价修饰系统对于自噬的发生至关重要。Apg12是一种含186个氨基酸的蛋白质，其羧基末端甘氨酸残基与Apg5（一种含294个氨基酸的蛋白质）第149位的赖氨酸残基缀合。在apg突变体中，我们发现apg7和apg10无法形成Apg5/Apg12缀合物。通过克隆APG7，我们发现Apg7是一种类泛素-E1酶。这种缀合可以在体外重建，并且依赖于ATP。据我们所知，这是关于一种与泛素无关的蛋白质使用类泛素化缀合系统的首次报道。此外，Apg5和Apg12在哺乳动物中有同源物，这表明这种新的修饰系统从酵母到哺乳动物细胞都是保守的。
