Institute of Biochemistry, Biological Research Centre of the Hungarian Academy of Sciences, H-6701 Szeged, Hungary.
Biochemistry. 2012 Mar 27;51(12):2461-70. doi: 10.1021/bi3001006. Epub 2012 Mar 15.
Analysis of the in vivo ubiquitylation of the p54/Rpn10 polyubiquitin receptor subunit of the Drosophila 26S proteasome revealed that the site of ubiquitylation is the C-terminal cluster of lysines, which is conserved in higher eukaryotes. Extraproteasomal p54 was extensively multiubiquitylated, but only very modest modification was detected in the proteasome-assembled subunit. Ubiquitylation of p54 seriously jeopardizes one of its most important functions, i.e., the interaction of its ubiquitin-interacting motifs with the ubiquitin-like domain of Dsk2 and Rad23 extraproteasomal polyubiquitin receptors. This modification of p54 supports the previous notion that p54 is a shuttling subunit of the 26S proteasome with a specific extraproteasomal function. This assumption is supported by the observation that, while transgenic p54 can fully rescue the lethal phenotype of the Δp54 null mutation, its derivative from which the cluster of conserved lysines is deleted shifts the lethality from the early pupa to pharate adult stage but cannot rescue the Δp54 mutation, suggesting that ubiquitylated extraproteasomal p54 has an essential role in the pupa-adult transition.
对果蝇 26S 蛋白酶体的 p54/Rpn10 多泛素受体亚基的体内泛素化分析表明，泛素化位点是 C 末端赖氨酸簇，该簇在高等真核生物中保守。额外蛋白酶体的 p54 被广泛多泛素化，但在组装好的蛋白酶体亚基中仅检测到适度的修饰。p54 的泛素化严重危及到其最重要的功能之一，即其泛素相互作用基序与 Dsk2 和 Rad23 额外蛋白酶体多泛素受体的泛素样结构域的相互作用。p54 的这种修饰支持了 p54 是 26S 蛋白酶体的穿梭亚基并具有特定的额外蛋白酶体功能的先前观点。这一假设得到了以下观察结果的支持：尽管转基因 p54 可以完全挽救 Δp54 缺失突变的致死表型，但缺失保守赖氨酸簇的衍生物将致死性从早期蛹转变为若虫成虫阶段，但不能挽救 Δp54 突变，表明额外蛋白酶体的泛素化 p54 在蛹-成虫过渡中具有重要作用。
