Lee Brittany J, Cansizoglu Ahmet E, Süel Katherine E, Louis Thomas H, Zhang Zichao, Chook Yuh Min
Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park, Dallas, TX 75390, USA.
Cell. 2006 Aug 11;126(3):543-58. doi: 10.1016/j.cell.2006.05.049.
Karyopherinbeta (Kapbeta) proteins bind nuclear localization and export signals (NLSs and NESs) to mediate nucleocytoplasmic trafficking, a process regulated by Ran GTPase through its nucleotide cycle. Diversity and complexity of signals recognized by Kap betas have prevented prediction of new Kap beta substrates. The structure of Kap beta 2 (also known as Transportin) bound to one of its substrates, the NLS of hnRNP A1, that we report here explains the mechanism of substrate displacement by Ran GTPase. Further analyses reveal three rules for NLS recognition by Kap beta 2: NLSs are structurally disordered in free substrates, have overall basic character, and possess a central hydrophobic or basic motif followed by a C-terminal R/H/KX(2-5)PY consensus sequence. We demonstrate the predictive nature of these rules by identifying NLSs in seven previously known Kap beta 2 substrates and uncovering 81 new candidate substrates, confirming five experimentally. These studies define and validate a new NLS that could not be predicted by primary sequence analysis alone.
核转运蛋白β（Kapβ）家族蛋白通过结合核定位信号和核输出信号（NLS和NES）来介导核质运输，这一过程受Ran GTP酶核苷酸循环的调控。由于Kapβ所识别信号的多样性和复杂性，人们难以预测新的Kapβ底物。我们在此报道的与Kapβ2（也称为转运蛋白）及其一种底物hnRNP A1的NLS相结合的结构，解释了Ran GTP酶置换底物的机制。进一步分析揭示了Kapβ2识别NLS的三条规则：NLS在游离底物中结构无序，具有整体碱性特征，并且拥有一个中央疏水或碱性基序，随后是一个C端R/H/KX(2 - 5)PY共有序列。我们通过在七个先前已知的Kapβ2底物中鉴定NLS并发现81个新的候选底物，其中五个经实验确认，证明了这些规则的预测性。这些研究定义并验证了一个仅通过一级序列分析无法预测的新NLS。
