Johnston S C, Riddle S M, Cohen R E, Hill C P
Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA.
EMBO J. 1999 Jul 15;18(14):3877-87. doi: 10.1093/emboj/18.14.3877.
The release of ubiquitin from attachment to other proteins and adducts is critical for ubiquitin biosynthesis, proteasomal degradation and other cellular processes. De-ubiquitination is accomplished in part by members of the UCH (ubiquitin C-terminal hydrolase) family of enzymes. We have determined the 2.25 A resolution crystal structure of the yeast UCH, Yuh1, in a complex with the inhibitor ubiquitin aldehyde (Ubal). The structure mimics the tetrahedral intermediate in the reaction pathway and explains the very high enzyme specificity. Comparison with a related, unliganded UCH structure indicates that ubiquitin binding is coupled to rearrangements which block the active-site cleft in the absence of authentic substrate. Remarkably, a 21-residue loop that becomes ordered upon binding Ubal lies directly over the active site. Efficiently processed substrates apparently pass through this loop, and constraints on the loop conformation probably function to control UCH specificity.
泛素从与其他蛋白质及加合物的附着状态释放，对于泛素生物合成、蛋白酶体降解及其他细胞过程至关重要。去泛素化部分由UCH（泛素C末端水解酶）家族的酶成员完成。我们已确定酵母UCH Yuh1与抑制剂泛素醛（Ubal）复合物的晶体结构，分辨率为2.25埃。该结构模拟了反应途径中的四面体中间体，并解释了极高的酶特异性。与相关的未结合配体的UCH结构比较表明，泛素结合与重排相偶联，在没有真实底物的情况下会阻塞活性位点裂缝。值得注意的是，一个在结合Ubal时变得有序的21个残基的环直接位于活性位点上方。经高效加工的底物显然会穿过这个环，并且对环构象的限制可能起到控制UCH特异性的作用。
