Forwood Jade K, Lonhienne Thierry G, Marfori Mary, Robin Gautier, Meng Weining, Guncar Gregor, Liu Sai M, Stewart Murray, Carroll Bernard J, Kobe Bostjan
School of Biomedical Sciences, Charles Sturt University, Wagga Wagga 2650, Australia.
J Mol Biol. 2008 Nov 21;383(4):772-82. doi: 10.1016/j.jmb.2008.07.090. Epub 2008 Aug 7.
The asymmetric distribution of the nucleotide-bound state of Ran across the nuclear envelope is crucial for determining the directionality of nuclear transport. In the nucleus, Ran is primarily in the guanosine 5'-triphosphate (GTP)-bound state, whereas in the cytoplasm, Ran is primarily guanosine 5'-diphosphate (GDP)-bound. Conformational changes within the Ran switch I and switch II loops are thought to modulate its affinity for importin-beta. Here, we show that RanGDP and importin-beta form a stable complex with a micromolar dissociation constant. This complex can be dissociated by importin-beta binding partners such as importin-alpha. Surprisingly, the crystal structure of the Kap95p-RanGDP complex shows that Kap95p induces the switch I and II regions of RanGDP to adopt a conformation that resembles that of the GTP-bound form. The structure of the complex provides insights into the structural basis for the gradation of affinities regulating nuclear protein transport.
Ran核苷酸结合状态在核膜两侧的不对称分布对于确定核运输的方向性至关重要。在细胞核中，Ran主要处于鸟苷5'-三磷酸（GTP）结合状态，而在细胞质中，Ran主要处于鸟苷5'-二磷酸（GDP）结合状态。Ran开关I和开关II环内的构象变化被认为可调节其对输入蛋白β的亲和力。在此，我们表明RanGDP与输入蛋白β形成了具有微摩尔解离常数的稳定复合物。该复合物可被输入蛋白β结合伴侣如输入蛋白α解离。令人惊讶的是，Kap95p-RanGDP复合物的晶体结构表明，Kap95p诱导RanGDP的开关I和II区域采用类似于GTP结合形式的构象。该复合物的结构为调节核蛋白运输的亲和力分级的结构基础提供了见解。
