Akey C W
Department of Biophysics, Boston University School of Medicine, Ma 02118-2394, USA.
J Mol Biol. 1995 Apr 28;248(2):273-93. doi: 10.1016/s0022-2836(95)80050-6.
The nuclear pore complex (NPC) is strategically located at continuous junctions of the inner and outer nuclear membranes to catalyze macromolecular transport, without impending the diffusion of small molecules. In this paper, the structural plasticity of 4412 NPCs in isolated nuclear envelopes has been evaluated, utilizing correspondence analysis, classification and difference mapping. The data are grouped into seven clusters comprising two major groups, based on the degree of radial compaction within spokes and the symmetry of the inner spoke ring. The results have been correlated with differences in spoke domain packing observed in two published three-dimensional maps suggesting that symmetrical detergent-extracted NPCs are similar, but not identical to the most probable in vivo structure. A model is proposed in which spoke architecture is responsive to changes in the turgor pressure of the nuclear envelope. For example, detergent extraction may allow the outward facing domains of each spoke to adopt a radially-extended configuration while osmotic swelling may induce an inwards displacement, resulting in a radially compact spoke. Difference maps between approximately 822 symmetric projections of NPCs in membranes and after detergent-extraction have localized the nuclear envelope border. The data place limits on the radial and circumferential dimensions of diffusion channels (approximately 0 to 20 A x 190 A), proposed to reside at the pore periphery. The results confirm the observation that each spoke penetrates the nuclear envelope, linking up with the radial arms to form a "lumenal ring". Finally, putative closed, open and in-transit forms of the transporter are found with the same relative frequency in membrane-associated NPCs with radially compact or extended spokes; hence spoke deformations in isolated envelopes may be induced by experimental factors. However, concerted movements of the spoke domains (if reversible) may be utilized in the biological function of the NPC and some examples are given.
核孔复合体（NPC）位于内核膜和外核膜的连续连接处，在不阻碍小分子扩散的情况下催化大分子运输。在本文中，利用对应分析、分类和差异映射评估了分离核膜中4412个NPC的结构可塑性。根据辐条内的径向压实程度和内辐条环的对称性，数据被分为七个簇，包括两个主要组。研究结果与在两份已发表的三维图谱中观察到的辐条结构域堆积差异相关，表明经去污剂提取的对称NPC相似，但与最可能的体内结构并不完全相同。本文提出了一个模型，其中辐条结构对核膜膨压的变化有响应。例如，去污剂提取可能使每个辐条向外的结构域呈径向延伸构型，而渗透肿胀可能诱导向内位移，导致辐条径向压实。膜中NPC与去污剂提取后的约822个对称投影之间的差异映射确定了核膜边界。这些数据限制了推测位于孔周边的扩散通道的径向和周向尺寸（约0至20埃×190埃）。研究结果证实了每个辐条穿透核膜并与径向臂相连形成“腔内环”的观察结果。最后，在辐条径向压实或延伸的膜相关NPC中，发现转运体的假定封闭、开放和转运形式具有相同的相对频率；因此，分离膜中的辐条变形可能是由实验因素诱导的。然而，辐条结构域的协同运动（如果是可逆的）可能在NPC的生物学功能中发挥作用，并给出了一些例子。
