顶科协奖获奖者讲堂：FG相与核孔的转运选择性

发布日期 2022年11月18日

在11月3日至7日于上海举行的第五届世界顶尖科学家论坛期间，世界顶尖科学家协会奖举办了获奖者讲堂系列讲座。11月7日，首届顶科协奖生命科学或医学奖获奖者迪尔克·格尔利希教授进行了学术演讲，其演讲的题目是：The FG phase and transport selectivity of nuclear pores（FG相与核孔的转运选择性）。讲座以直播方式进行。

演讲摘要:

Cells of eukaryotic organisms (such as animals) rely on sophisticated logistics, including compartments that fulfill distinct functions and therefore use different sets of enzymes. The nucleus harbors the genome, transcribes DNA into RNA, and assembles and exports ribosomes. However, it must import all needed proteins from the cytoplasm, which is specialized in protein synthesis. This nucleocytoplasmic exchange proceeds through nuclear pore complexes (NPCs) that allow a (slow) passive passage as well as (rapid) active, facilitated transport.

Our lab has a long-standing interest in the underlying mechanisms. We discovered importins and exportins (collectively called nuclear transport receptors or NTRs for short), which import cargoes into and export others out of cell nuclei. We established that active transport by importins and exportins is powered by a nucleocytoplasmic RanGTP gradient and that importins also function as chaperones, protecting sticky cargoes during transit from ionic aggregation.

Another key observation was the enormous transport capacity of NPCs, which can each translocate ≈ 1000 NTR molecules or a mass equivalent of 100 Megadalton (MDa) per second. At the same time, NPCs function as barriers that prevent intermixing of nuclear and cytoplasmic contents. We discovered that the permeability barrier of NPCs is a hydrogel-like ‘FG phase’, repelling normal (‘inert’) macromolecules but being an excellent ‘solvent’ for NTRs and their cargo complexes. Transport through NPCs can thus be described as mobile species partitioning into this FG phase and exiting on the opposite side. This FG phase self-assembles from intrinsically disordered FG repeat domains, with hydrophobic phenylalanine-glycine (FG) motifs engaging in highly multivalent, cohesive interactions. This multivalency results in a 3D sieve whose mesh size rules the (passive) sieving properties of the phase. NTRs bind FG motifs, compete FG-FG interactions locally, and can thus ‘melt’ (along with their cargoes) through the meshes. We recently asked for the simplest possible implementation of a selective FG phase and found a perfectly repeated, 12mer GLFG peptide to be sufficient for phase assembly, barrier function, and facilitated transport of all tested NTR-cargo complexes. This extreme simplicity of the basic NPC function strikingly contrasts the elaborate structure of the 100 MDa NPC scaffold.

The FG phase initially seemed an exotic state of biological matter; however, it just pre-figured the exciting observations of the now rapidly expanding field of cellular phase transitions/ liquid-liquid phase separations, which are also driven by similar multivalent interactions between intrinsically disordered protein domains.

（中文译稿仅供参考，以英文原文为准）

真核生物（如动物）细胞内物质的运输及分配依赖其复杂的物流系统，比如细胞区室，确保细胞能够同时进行不同的代谢活动并使用不同的酶组。细胞核蕴含基因组，将DNA转录成RNA，组装并输出核糖体。然而，然而，它必须从专门从事蛋白质合成的细胞质中导入所有需要的蛋白质。它必须从细胞质——蛋白质合成发生的地方输入所有需要的蛋白质。这种细胞核质转运通过核孔复合体（NPC）进行，允许（缓慢的）被动扩散以及（快速）主动、快速运输。

我们实验室对其潜在机制进行了长期研究，发现了将货物蛋白输入到细胞核，并将其他货物从细胞核中输出的输入和输出蛋白（统称为核质转运受体或简称为NTR）。研究确定，输入蛋白和输出蛋白的主动转运的能量主要由细胞核内与细胞质之间的RanGTP梯度提供，同时，输入蛋白也起到了分子伴侣的作用，在转运过程中保护粘性货物蛋白免受离子聚集的影响。

另一项主要发现是NPC的巨大转运能力，每秒可转运约1000个 NTR分子或相当于分子质量达100兆道尔顿（MDa）。同时，NPC作为物理屏障，阻止核、质内物质的混合。我们发现，NPC的渗透屏障是一种水凝胶状的“FG相”，保留了惰性大分子，但对于蛋白复合体来说是一种极好的“溶剂”，允许导入和导出蛋白的通过，从而使货物穿梭进出细胞核。屏障可以描述为由粘性 FG 重复结构域组装而成的凝聚相，充分参与多价态的内聚合反应。多价态性可形成3D筛，其筛孔尺寸决定相的（被动）筛分特性。NTR与相邻FG域对FG域点位的竞争，导致蛋白复合体凝聚态的形成。最近，我们成功地设计了一个完美重复的12聚体GLFG肽，该肽自组装成具有精细运输选择性和快速运输动力学的屏障。该屏障概括了 RanGTPase 控制的导入和导出介导的货物运输，因此代表了最终简化的实验模型系统。

FG相最初被视作一种生物异质相；但事实上，它预先揭示了目前正迅速扩展的细胞相变/液-液分离这一研究领域的重要成果，即这也是由内在的无序蛋白质结构域之间类似的多价相互作用下形成的。