Functional Asymmetries of Proteasome Translocase Pore
Functional Asymmetries of Proteasome Translocase Pore
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DOI：
10.1074/jbc.m112.357327
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发表时间：
2012-05-25
影响因子：
4.8
通讯作者：
Coffino, Philip
中科院分区：
文献类型：
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作者：
Erales, Jenny;Hoyt, Martin A.;Coffino, Philip
蛋白酶体降解涉及偶联易位和解折叠的蛋白质底物。六种不同但平行的蛋白酶体ATP酶蛋白Rpt 1至-6形成作用于底物的异六聚体环。轴向定位的环（Ar-Phi环）与ATP水解一致地移动，接合底物，并将其推进蛋白水解室。S的所有六个Rpts中Ar-Phi环的芳族（Ar）残基。酿酒酵母中的氨基酸是酪氨酸;这种氨基酸被认为与底物具有重要的功能接触。构建并表征了其中Tyr单独突变为Ala的六种酵母菌株。突变体细胞是活的并且具有不同的表型。rpt 3，rpt 4和rpt 5 Tyr/Ala突变体，簇在ATP酶六聚体的一侧，在其降解底物的能力大大受损。相反，rpt 1，rpt 2和rpt 6突变体的降解活性等于或超过野生型。然而，rpt 1和rpt 6突变体的缺陷，限制细胞生长或生存能力的条件下，强调泛素蛋白酶体系统。相比之下，rpt 3突变体比野生型生长更快，尺寸更小，这是一种以前与G1细胞周期蛋白失调相关的缺陷。这种rpt 3表型可能是由细胞周期调节蛋白降解改变引起的。最后，5个Rpt亚基的突变增加了蛋白酶体ATP酶活性，这意味着Ar-Phi环和ATP水解位点之间的双向偶联。目前的观察分配特定的功能，个别RPT蛋白，并提供见解的轴向循环的不同作用的个别蛋白酶体ATP酶。
Degradation by proteasomes involves coupled translocation and unfolding of its protein substrates. Six distinct but paralo-gous proteasome ATPase proteins, Rpt1 to -6, form a heterohexameric ring that acts on substrates. An axially positioned loop (Ar-Phi loop) moves in concert with ATP hydrolysis, engages substrate, and propels it into a proteolytic chamber. The aromatic (Ar) residue of the Ar-Phi loop in all six Rpts of S. cerevisiae is tyrosine; this amino acid is thought to have important functional contacts with substrate. Six yeast strains were constructed and characterized in which Tyr was individually mutated to Ala. The mutant cells were viable and had distinct phenotypes. rpt3, rpt4, and rpt5 Tyr/Ala mutants, which cluster on one side of the ATPase hexamer, were substantially impaired in their capacity to degrade substrates. In contrast, rpt1, rpt2, and rpt6 mutants equaled or exceeded wild type in degradation activity. However, rpt1 and rpt6 mutants had defects that limited cell growth or viability under conditions that stressed the ubiquitin proteasome system. In contrast, the rpt3 mutant grew faster than wild type and to a smaller size, a defect that has previously been associated with misregulation of G1 cyclins. This rpt3 phenotype probably results from altered degradation of cell cycle regulatory proteins. Finally, mutation of five of the Rpt subunits increased proteasome ATPase activity, implying bidirectional coupling between the Ar-Phi loop and the ATP hydrolysis site. The present observations assign specific functions to individual Rpt proteins and provide insights into the diverse roles of the axial loops of individual proteasome ATPases.