Rahighi Simin, Braunstein Ilana, Ternette Nicola, Kessler Benedikt, Kawasaki Masato, Kato Ryuichi, Matsui Tsutomu, Weiss Thomas M, Stanhill Ariel, Wakatsuki Soichi
Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan; Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Department of Biochemistry, Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Bat Galim, Haifa 31096, Israel.
Structure. 2016 Mar 1;24(3):412-22. doi: 10.1016/j.str.2015.12.017. Epub 2016 Feb 11.
Lys48-linked ubiquitin chains act as the main targeting signals for protein degradation by the proteasome. Here we report selective binding of AIRAPL, a protein that associates with the proteasome upon exposure to arsenite, to Lys48-linked tri-ubiquitin chains. AIRAPL comprises two ubiquitin-interacting motifs in tandem (tUIMs) that are linked through a flexible inter-UIM region. In the complex crystal structure UIM1 binds the proximal ubiquitin, whereas UIM2 (the double-sided UIM) binds non-symmetrically to the middle and distal ubiquitin moieties on either side of the helix. Specificity of AIRAPL for Lys48-linked ubiquitin chains is determined by UIM2, and the flexible inter-UIM linker increases avidity by placing the two UIMs in an orientation that facilitates binding of the third ubiquitin to UIM1. Unlike middle and proximal ubiquitins, distal ubiquitin binds UIM2 through a novel surface, which leaves the Ile44 hydrophobic patch accessible for binding to the proteasomal ubiquitin receptors.
赖氨酸48连接的泛素链作为蛋白酶体进行蛋白质降解的主要靶向信号。在此我们报告了AIRAPL（一种在暴露于亚砷酸盐时与蛋白酶体结合的蛋白质）与赖氨酸48连接的三聚泛素链的选择性结合。AIRAPL包含两个串联的泛素相互作用基序（tUIMs），它们通过一个灵活的UIM间区域相连。在复合物晶体结构中，UIM1结合近端泛素，而UIM2（双面UIM）不对称地结合螺旋两侧的中间和远端泛素部分。AIRAPL对赖氨酸48连接的泛素链的特异性由UIM2决定，灵活的UIM间连接子通过将两个UIM以一种便于第三个泛素与UIM1结合的方向排列来增加亲和力。与中间和近端泛素不同，远端泛素通过一个新的表面结合UIM2，这使得异亮氨酸44疏水补丁可用于与蛋白酶体泛素受体结合。
