Characterization of the Importin-β binding domain in nuclear import receptor KPNA7
Characterization of the Importin-β binding domain in nuclear import receptor KPNA7
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DOI：
10.1042/bcj20190717
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发表时间：
2019-11-01
影响因子：
4.1
通讯作者：
Paschal, Bryce M.
中科院分区：
文献类型：
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作者：
Oostdyk, Luke T.;McConnell, Michael J.;Paschal, Bryce M.
哺乳动物核输入受体的KPNA家族由七个基因编码，这些基因产生具有42-86%同一性的同种型。KPNA亚型具有相同的蛋白质结构，并共享核定位信号（NLS）识别的功能特性，然而，这些受体的组织和发育表达模式提出了一个问题，即KPNA亚型的细微差异是否在特定的生物学背景下可能是重要的。在这里，我们表明，KPNA 7，表达主要限于早期发展的亚型，可以结合输入-β（Imp-beta）的NLS货物的情况下。该结果与Imp-beta与其他KPNA家族成员的相互作用形成对比，其中亲和力由NLS货物调节，作为合作结合机制的一部分。在所有KPNA家族成员中高度保守的Imp-beta结合（伊布）结构域通常用于封闭NLS结合沟并在NLS接触之前将受体维持在自抑制的“闭合”状态。NLS货物和Imp-beta与KPNA的协同结合导致“开放”状态。KPNA 2-KPNA 7嵌合蛋白的表征表明，伊布结构域和受体核心结构的特征有助于伊布结构域对Imp-beta结合的可及性程度，这可能反映了“开放”状态。我们还提供了KPNA 7在细胞核中保持开放状态的证据。我们推测KPNA 7可能通过与含NLS的蛋白相互作用在细胞核内发挥作用。
The KPNA family of mammalian nuclear import receptors are encoded by seven genes that generate isoforms with 42-86% identity. KPNA isoforms have the same protein architecture and share the functional property of nuclear localization signal (NLS) recognition, however, the tissue and developmental expression patterns of these receptors raise the question of whether subtle differences in KPNA isoforms might be important in specific biological contexts. Here, we show that KPNA7, an isoform with expression mostly limited to early development, can bind Importin-beta (Imp-beta) in the absence of NLS cargo. This result contrasts with Imp-beta interactions with other KPNA family members, where affinity is regulated by NLS cargo as part of a cooperative binding mechanism. The Imp-beta binding (IBB) domain, which is highly conserved in all KPNA family members, generally serves to occlude the NLS binding groove and maintain the receptor in an auto-inhibited 'closed' state prior to NLS contact. Cooperative binding of NLS cargo and Imp-beta to KPNA results in an 'open'state. Characterization of KPNA2-KPNA7 chimeric proteins suggests that features of both the IBB domain and the core structure of the receptor contribute to the extent of IBB domain accessibility for Imp-beta binding, which likely reflects an 'open' state. We also provide evidence that KPNA7 maintains an open-state in the nucleus. We speculate that KPNA7 could function within the nucleus by interacting with NLS-containing proteins.