Technion-IIT, Department of Molecular Microbiology, B. Rappaport Faculty of Medicine, 2 Efron St., Haifa 31096, Israel.
Mol Cell Biol. 2010 Feb;30(4):985-94. doi: 10.1128/MCB.00909-09. Epub 2009 Dec 14.
The 26S proteasome is a large cytoplasmic protease that degrades polyubiquitinated proteins to short peptides in a processive manner. The proteasome 19S regulatory subcomplex tethers the target protein via its polyubiquitin adduct and unfolds the target polypeptide, which is then threaded into the proteolytic site-containing 20S subcomplex. Hul5 is a 19S subcomplex-associated ubiquitin ligase that elongates ubiquitin chains on proteasome-bound substrates. We isolated hul5 Delta as a mutation with which fusions of an unstable cyclin to stable reporter proteins accumulate as partially processed products. These products appear transiently in the wild type but are strongly stabilized in 19S ATPase mutants and in the hul5 Delta mutant, supporting a role for the ATPase subunits in the unfolding of proteasome substrates before insertion into the catalytic cavity and suggesting a role for Hul5 in the processive degradation of proteins that are stalled on the proteasome.
26S 蛋白酶体是一种大型细胞质蛋白酶，以连续的方式将多泛素化蛋白降解为短肽。蛋白酶体 19S 调节亚基通过其多泛素加合物将靶蛋白连接，并展开靶多肽，然后将其穿入含有蛋白酶体的 20S 亚基。Hul5 是一种与 19S 亚基相关的泛素连接酶，可在蛋白酶体结合的底物上延长泛素链。我们分离出 hul5Δ作为一种突变，不稳定的细胞周期蛋白与稳定的报告蛋白融合会积累为部分加工产物。这些产物在野生型中短暂出现，但在 19S ATP 酶突变体和 hul5Δ突变体中被强烈稳定，这支持 ATP 酶亚基在插入催化腔之前将蛋白酶体底物展开的作用，并表明 Hul5 在蛋白酶体上停滞的蛋白质的连续降解中发挥作用。
