Biochemistry Department, University of Otago, Dunedin 9054, New Zealand.
J Mol Biol. 2013 Nov 15;425(22):4099-111. doi: 10.1016/j.jmb.2013.06.039. Epub 2013 Jul 17.
Protein ubiquitylation depends upon the concerted action of ubiquitin-conjugating enzymes (E2s) and ubiquitin ligases (E3s). All E2s have a conserved ubiquitin-conjugating (UBC) domain but many have variable extensions N- and C-terminal to the UBC domain. For many E2s, the function of the extension is not well understood. Here, we show that the N-terminal extension of the UBE2E proteins regulates formation of polyubiquitin chains by the processive UBC domain. Target proteins are therefore monoubiquitylated by full-length UBE2E, whereas the UBC domain alone polyubiquitylates proteins. Although the N-terminal extension of UBE2E1 is largely disordered in solution, these residues have a critical role in limiting chain building, and when fused to the highly processive E2, UBE2D2, ubiquitylation is limited. For some E2s, interaction of ubiquitin with the 'backside' of the UBC domain promotes polyubiquitylation. However, interaction of ubiquitin with the backside of the UBC domain of UBE2E1 does not appear to be important for processivity. This study underscores the importance of studying full-length E2 proteins and not just the highly conserved core domain.
蛋白质泛素化依赖于泛素结合酶（E2s）和泛素连接酶（E3s）的协同作用。所有 E2s 都具有保守的泛素结合（UBC）结构域，但许多 E2s 在 UBC 结构域的 N 端和 C 端具有可变的延伸。对于许多 E2s 来说，延伸的功能还不是很清楚。在这里，我们表明 UBE2E 蛋白的 N 端延伸通过连续的 UBC 结构域调节多泛素链的形成。因此，全长 UBE2E 将靶蛋白单泛素化，而 UBC 结构域本身则多泛素化蛋白。尽管 UBE2E1 的 N 端延伸在溶液中大部分是无规卷曲的，但这些残基在限制链构建中起着关键作用，并且当与高度连续的 E2，UBE2D2 融合时，泛素化受到限制。对于一些 E2s，泛素与 UBC 结构域“背面”的相互作用促进多泛素化。然而，泛素与 UBE2E1 的 UBC 结构域背面的相互作用似乎对连续性不重要。这项研究强调了研究全长 E2 蛋白而不仅仅是高度保守的核心结构域的重要性。
