A new protein conjugation system in human - The counterpart of the yeast Apg12p conjugation system essential for autophagy
A new protein conjugation system in human - The counterpart of the yeast Apg12p conjugation system essential for autophagy
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DOI：
10.1074/jbc.273.51.33889
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发表时间：
1998-12-18
影响因子：
4.8
通讯作者：
Ohsumi, Y
中科院分区：
文献类型：
--
作者：
Mizushima, N;Sugita, H;Ohsumi, Y
自噬是细胞内大量降解细胞质成分的过程。我们最近发现了一个蛋白质结合系统的自噬在酵母，酿酒酵母。新型修饰蛋白Apg 12 p的C-末端甘氨酸通过异肽珠与Apg 5 p的赖氨酸残基缀合。该缀合反应由Apg 7 p（一种泛素活化酶（E1）样酶）和Apg 10 p介导，表明它是一种泛素化样系统（Mizushima，N.，野田，T.，Yoshimori，T.，Tanaka，Y.，石井，T.，乔治，M. D、克里昂斯基，D。J，，Ohsumi，Ri.，和Ohsumi，Y.（1998）Nature 395，395-398）。虽然自噬是真核细胞中普遍存在的过程，但在高等真核生物中还没有鉴定出参与自噬的分子。我们推断这个共轭系统是保守的。在这里，我们报告的克隆和鉴定的人类同源Apg 12（hApg 12）。它是一个由140个氨基酸组成的蛋白质，与酵母Apg 12 p具有27%的同源性和48%的相似性，但与泛素没有明显的同源性。北方印迹分析表明，其在人体组织中普遍表达。我们发现它与另一种蛋白质共价连接。该靶蛋白被鉴定为人Apg 5同源物（hApg 5）。突变分析表明，这种结合是通过hApg 12的C-末端甘氨酸和hApg 5的Lys-130之间的异肽键形成的。这些发现表明Apg 12系统是非常保守的，并且可能在人类细胞中也在自噬中起作用。
Autophagy is an intracellular process for bulk degradation of cytoplasmic components. We recently found a protein conjugation system essential for autophagy in the yeast, Saccharomyces cerevisiae. The C-terminal glycine of a novel modifier protein, Apg12p, is conjugated to a lysine residue of Apg5p via an isopeptide bead. This conjugation reaction is mediated by Apg7p, a ubiquitin activating enzyme (E1)-like enzyme, and Apg10p, suggesting that it is a ubiquitination-like system (Mizushima, N., Noda, T., Yoshimori, T., Tanaka, Y., Ishii, T., George, M. D., Klionsky, D. J,, Ohsumi, Ri., and Ohsumi, Y. (1998) Nature 395, 395-398). Although autophagy is a ubiquitous process in eukaryotic cells, no molecule involved in autophagy has yet been identified in higher eukaryotes. We reasoned that this conjugation system could be conserved. Here we report cloning and characterization of the human homologue of Apg12 (hApg12). It is a 140-amino acid protein and possesses 27% identity and 48% similarity with the yeast Apg12p, but no apparent homology to ubiquitin. Northern blot analysis showed that its expression was ubiquitous in human tissues. We found that it was covalently attached to another protein. This target protein was identified to be the human Apg5 homologue (hApg5). Mutagenic analyses suggested that this conjugation was formed via an isopeptide bond between the C-terminal glycine of hApg12 and Lys-130 of hApg5. These findings indicate that the Apg12 system is well conserved and may function in autophagy also in human cells.