Fontes M R, Teh T, Kobe B
Structural Biology Laboratory, St. Vincent's Institute of Medical Research, 41 Victoria Parade, Fitzroy, Victoria 3065, Australia.
J Mol Biol. 2000 Apr 14;297(5):1183-94. doi: 10.1006/jmbi.2000.3642.
Importin-alpha is the nuclear import receptor that recognizes cargo proteins which contain classical monopartite and bipartite nuclear localization sequences (NLSs), and facilitates their transport into the nucleus. To determine the structural basis of the recognition of the two classes of NLSs by mammalian importin-alpha, we co-crystallized an N-terminally truncated mouse receptor protein with peptides corresponding to the monopartite NLS from the simian virus 40 (SV40) large T-antigen, and the bipartite NLS from nucleoplasmin. We show that the monopartite SV40 large T-antigen NLS binds to two binding sites on the receptor, similar to what was observed in yeast importin-alpha. The nucleoplasmin NLS-importin-alpha complex shows, for the first time, the mode of binding of bipartite NLSs to the receptor. The two basic clusters in the NLS occupy the two binding sites used by the monopartite NLS, while the sequence linking the two basic clusters is poorly ordered, consistent with its tolerance to mutations. The structures explain the structural basis for binding of diverse NLSs to the sole receptor protein.
输入蛋白α是一种核输入受体，可识别含有典型单分型和双分型核定位序列（NLSs）的货物蛋白，并促进它们转运到细胞核中。为了确定哺乳动物输入蛋白α识别这两类NLSs的结构基础，我们将一种N端截短的小鼠受体蛋白与对应于猿猴病毒40（SV40）大T抗原的单分型NLS以及核纤层蛋白的双分型NLS的肽段进行了共结晶。我们发现，单分型的SV40大T抗原NLS与受体上的两个结合位点结合，这与在酵母输入蛋白α中观察到的情况类似。核纤层蛋白NLS-输入蛋白α复合物首次展示了双分型NLSs与受体的结合模式。NLS中的两个碱性簇占据了单分型NLS所使用的两个结合位点，而连接两个碱性簇的序列无序性较高，这与其对突变的耐受性一致。这些结构解释了不同NLSs与单一受体蛋白结合的结构基础。
