Bays N W, Gardner R G, Seelig L P, Joazeiro C A, Hampton R Y
Section of Cell and Developmental Biology, Division of Biology, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0347, USA.
Nat Cell Biol. 2001 Jan;3(1):24-9. doi: 10.1038/35050524.
In eukaryotes, endoplasmic reticulum-associated degradation (ERAD) functions in cellular quality control and regulation of normal ER-resident proteins. ERAD proceeds by the ubiquitin-proteasome pathway, in which the covalent attachment of ubiquitin to proteins targets them for proteasomal degradation. Ubiquitin-protein ligases (E3s) play a crucial role in this process by recognizing target proteins and initiating their ubiquitination. Here we show that Hrd1p, which is identical to Der3p, is an E3 for ERAD. Hrd1p is required for the degradation and ubiquitination of several ERAD substrates and physically associates with relevant ubiquitin-conjugating enzymes (E2s). A soluble Hrd1 fusion protein shows E3 activity in vitro - catalysing the ubiquitination of itself and test proteins. In this capacity, Hrd1p has an apparent preference for misfolded proteins. We also show that Hrd1p functions as an E3 in vivo, using only Ubc7p or Ubc1p to specifically program the ubiquitination of ERAD substrates.
在真核生物中，内质网相关降解（ERAD）在细胞质量控制和正常内质网驻留蛋白的调节中发挥作用。ERAD通过泛素-蛋白酶体途径进行，其中泛素与蛋白质的共价连接将它们靶向蛋白酶体降解。泛素-蛋白质连接酶（E3s）通过识别靶蛋白并启动其泛素化在这一过程中起关键作用。在这里，我们表明与Der3p相同的Hrd1p是ERAD的E3。Hrd1p是几种ERAD底物降解和泛素化所必需的，并且与相关的泛素结合酶（E2s）物理结合。一种可溶性Hrd1融合蛋白在体外显示出E3活性——催化自身和测试蛋白的泛素化。以此能力，Hrd1p明显偏好错误折叠的蛋白。我们还表明，Hrd1p在体内作为E3发挥作用，仅使用Ubc7p或Ubc1p来特异性地编程ERAD底物的泛素化。
