Lenk Uwe, Yu Helen, Walter Jan, Gelman Marina S, Hartmann Enno, Kopito Ron R, Sommer Thomas
The Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Str. 10, 13092 Berlin, Germany.
J Cell Sci. 2002 Jul 15;115(Pt 14):3007-14. doi: 10.1242/jcs.115.14.3007.
Integral membrane and secretory proteins which fail to fold productively are retained in the endoplasmic reticulum and targeted for degradation by cytoplasmic proteasomes. Genetic and biochemical analyses suggest that substrates of this pathway must be dislocated across the membrane of the endoplasmic reticulum (ER) by a process requiring a functional Sec61 complex and multiubiquitinylation. In yeast, the tail-anchored ubiquitin-conjugating enzyme Ubc6p, which is localized to the cytoplasmic surface of the ER, participates in ER-associated degradation (ERAD) of misfolded proteins. Here we describe the identification of two families of mammalian Ubc6p-related proteins. Members of both families are also located in the ER membrane and display a similar membrane topology as the yeast enzyme. Furthermore we show that expression of elevated levels of wild-type and dominant-negative alleles of these components affects specifically ERAD of the alpha subunit of the T-cell receptor and a mutant form of the CFTR protein. Similarly, we describe that the expression level of Ubc6p in yeast is also critical for ERAD, suggesting that the Ubc6p function is highly conserved from yeast to mammals.
无法有效折叠的整合膜蛋白和分泌蛋白会被滞留在内质网中，并被细胞质蛋白酶体靶向降解。遗传和生化分析表明，该途径的底物必须通过一个需要功能性Sec61复合体和多聚泛素化的过程跨内质网（ER）膜移位。在酵母中，定位于内质网细胞质表面的尾锚定泛素结合酶Ubc6p参与错误折叠蛋白的内质网相关降解（ERAD）。在此，我们描述了两类哺乳动物Ubc6p相关蛋白的鉴定。这两个家族的成员也位于内质网膜中，并且与酵母酶具有相似的膜拓扑结构。此外，我们表明这些组分的野生型和显性负等位基因的高水平表达会特异性地影响T细胞受体α亚基和CFTR蛋白突变形式的ERAD。同样，我们描述了酵母中Ubc6p的表达水平对ERAD也至关重要，这表明从酵母到哺乳动物，Ubc6p的功能高度保守。
