School of Dentistry and Medical Sciences, Charles Sturt University, Wagga Wagga, NSW, 2678, Australia.
School of Dentistry and Medical Sciences, Charles Sturt University, Room 2, National Life Sciences Hub, Wagga Wagga, NSW, 2678, Australia.
Sci Rep. 2022 Jan 10;12(1):315. doi: 10.1038/s41598-021-03729-3.
Shuttling of macromolecules between nucleus and cytoplasm is a tightly regulated process mediated through specific interactions between cargo and nuclear transport proteins. In the classical nuclear import pathway, importin alpha recognizes cargo exhibiting a nuclear localization signal, and this complex is transported through the nuclear pore complex by importin beta. Humans possess seven importin alpha isoforms that can be grouped into three subfamilies, with many cargoes displaying specificity towards these importin alpha isoforms. The cargo binding sites within importin alpha isoforms are highly conserved in sequence, suggesting that specificity potentially relies on structural differences. Structures of some importin alpha isoforms, both in cargo-bound and free states, have been previously solved. However, there are currently no known structures of cargo free importin alpha isoforms within subfamily 3 (importin alpha 5, 6, 7). Here, we present the first crystal structure of human importin alpha 7 lacking the IBB domain solved at 2.5 Å resolution. The structure reveals a typical importin alpha architecture comprised of ten armadillo repeats and is most structurally conserved with importin alpha 5. Very little difference in structure was observed between the cargo-bound and free states, implying that importin alpha 7 does not undergo conformational change when binding cargo. These structural insights provide a strong platform for further evaluation of structure-function relationships and understanding how isoform specificity within the importin alpha family plays a role in nuclear transport in health and disease.
大分子在核与细胞质之间的穿梭是一个受到严格调控的过程，通过货物与核转运蛋白之间的特异性相互作用来介导。在经典的核输入途径中，importin α 识别具有核定位信号的货物，该复合物通过 importin β 被运送到核孔复合物中。人类有七种 importin α 异构体，可以分为三个亚家族，许多货物对这些 importin α 异构体具有特异性。importin α 异构体中的货物结合位点在序列上高度保守，这表明特异性可能依赖于结构差异。一些 importin α 异构体的结构，无论是在货物结合状态还是在游离状态下，都已经被解决。然而，目前还没有已知的亚家族 3（importin α5、6、7）中无货物结合的 importin α 异构体的结构。在这里，我们首次报道了缺乏 IBB 结构域的人源 importin α7 的晶体结构，分辨率为 2.5 Å。该结构揭示了一个典型的 importin α 结构，由十个臂状重复组成，与 importin α5 的结构最保守。货物结合和游离状态之间的结构差异很小，这意味着 importin α7 在结合货物时不会发生构象变化。这些结构见解为进一步评估结构-功能关系以及了解 importin α 家族内的同工型特异性如何在健康和疾病中的核转运中发挥作用提供了一个强有力的平台。
