Plant importin α vinds nuclear localization sequences with high affinity and can mediate nuclear import independent of importin β
Plant importin α vinds nuclear localization sequences with high affinity and can mediate nuclear import independent of importin β
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DOI：
10.1074/jbc.274.32.22610
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发表时间：
1999-08-06
影响因子：
4.8
通讯作者：
Jans, DA
中科院分区：
文献类型：
--
作者：
Hübner, S;Smith, HMS;Jans, DA
常规的含有核定位序列（NLS）的蛋白质的核输入最初涉及输入蛋白（IMP）odp异二聚体的识别，其中IMP α结合NLS，IMP β将含有IMP α/NLS的蛋白质复合物靶向核孔。在这里，我们研究IMP α从植物拟南芥（在IMP α），表现出典型的核包膜定位IMP β，而不是IMP α在其他真核细胞系统。我们表明，At-IMP α识别两种不同类型的常规NLS具有高亲和力（Kd为5-10 nM），与小鼠IMP α（m-IMP α）相反，其表现出低得多的亲和力（Kd为50-70 nM），并且仅在m-IMP β存在下实现高亲和力。与m-IMP α不同，At-IMP α因此是在不存在IMP β的情况下的高亲和力NLS受体。有趣的是，At-IMP α也能够以高亲和力结合由m-IMP β而不是m-IMP α特异性识别的NLS，包括玉米转录因子Opaque-2。体外重建核输入表明，在不存在外源性IMP β亚基但依赖于RanGDP和NTF 2的情况下，At-IMP α能够介导核蓄积至与m-IMP α/β介导的水平相当的水平。在没有其他亚基的情况下，m-IMP α和β都不能介导核输入。At-IMP α的新的NLS识别和核运输特性意味着植物可能具有IMP α介导的核输入途径独立于IMP β，除了由IMP α/β介导。
Nuclear import of conventional nuclear localization sequence (NLS)-containing proteins initially involves recognition by the importin (IMP) odp heterodimer, where IMP alpha binds the NLS and IMP beta targets the IMP alpha/NLS-containing protein complex to the nuclear pore. Here we examine IMP alpha from the plant Arabidopsis thaliana (At-IMP alpha), which exhibits nuclear envelope localization typical of IMP beta rather than IMP alpha in other eukaryotic cell systems. We show that At-IMP alpha recognizes conventional NLSs of two different types with high affinity (K-d of 5-10 nM), in contrast to mouse IMP alpha (m-IMP alpha), which exhibits much lower affinity (K-d of 50-70 nM) and only achieves high affinity in the presence of m-IMP beta. Unlike m-IMP alpha, At-IMP alpha is thus a high affinity NLS receptor in the absence of IMP beta. Interestingly, At-IMP alpha was also able to bind with high affinity to NLSs recognized specifically by m-IMP beta and not m-IMP alpha, including that of the maize transcription factor Opaque-2. Reconstitution of nuclear import in vitro indicated that in the absence of exogenous IMP beta subunit but dependent on RanGDP and NTF2, At-IMP alpha was able to mediate nuclear accumulation to levels comparable with those mediated by m-IMP alpha/beta. Neither m-IMP alpha nor -beta was able to mediate nuclear import in the absence of the other subunit. At-IMP alpha's novel NLS recognition and nuclear transport properties imply that plants may possess an IMP alpha-mediated nuclear import pathway independent of IMP beta in addition to that mediated by IMP alpha/beta.