Nanomechanical Basis of Selective Gating by the Nuclear Pore Complex

Abstract

The nuclear pore complex regulates cargo transport between the cytoplasm and the nucleus. We set out to correlate the governing biochemical interactions to the nanoscopic responses of the phenylalanineglycine (FG)-rich nucleoporin domains, which are involved in attenuating or promoting cargo translocation. We found that binding interactions with the transport receptor karyopherin-beta1 caused the FG domains of the human nucleoporin Nup153 to collapse into compact molecular conformations. This effect was reversed by the action of Ran guanosine triphosphate, which returned the FG domains into a polymer brush-like, entropic barrier conformation. Similar effects were observed in Xenopus oocyte nuclei in situ. Thus, the reversible collapse of the FG domains may play an important role in regulating nucleocytoplasmic transport.

How to operate a nuclear pore complex by Kap-centric control

“…At low Kapb1 concentrations, we found that Kapb1 molecules exhibited slow kinetic off rates due to strong Kap-FG Nup binding (K D 9 1 mM) that correlated with FG layer collapse. 21 Stepwise increases in Kapb1 concentrations then led to a gradual re-extension of the FG layer. 26,44,48 This socalled "self-healing" can be attributed to an increase in population (and volume) of bound Kapb1 within the FG layers, as predicted by Zilman theory.…”

“…Inevitably, in vitro-derived FG Nup materials, such as supramolecular hydrogel meshworks, 19,20 and molecular brushes, 21,22 or their proposed combinations 23 dominate how we treat the FG Nups as the key barrier components, as evident in artistic depictions of the NPC. Regardless, what is clear is that the FG Nups -being intrinsically disordered -are sensitive to experimental design in vitro, and can adopt different morphologies at different length scales with diverse structures, characteristics and properties.…”

“…21 A third ensued from results showing that the presence of Kaps helped to tighten the barrier against non-specific entities in artificial NPCs 46 and FG Nup gels. 47 Fourth, even non-specific molecules could modulate and weaken Kap-FG Nup binding.…”

Converging on the function of intrinsically disordered nucleoporins in the nuclear pore complex

“…The FG-domains would then be easily 'pushed aside' by transient Kap-FG interactions for cargo translocation to proceed. Indeed, the mobility of FG-domains has been inferred from immunolabeling electron microscopy based on variations in their localization within the NPC (Fahrenkrog et al, 2002;Lim et al, 2007a). Later, in vitro evidence obtained using biophysical atomic force microscope (AFM) measurements showed that the FG-domain of Nup153 could act collectively as a polymer brush when endtethered to 100 nm gold nanostructures (Lim et al, 2006(Lim et al, , 2007a.…”

“…In spite of their variety, these models differ only in the physical arrangement and mobility (static vs. dynamic) of the FGdomains within the NPC. So far, studies targeting the materials properties of the FG-domains directly show that FG-domain behavior can be classified as resembling (i) a polymer brush (Lim et al, 2006(Lim et al, , 2007aMiao and Schulten, 2009) (i.e., dynamic), (ii) a bulk-like hydrogel meshwork (Frey et al, 2006;Gorlich, 2007, 2009) (i.e., static) or (iii) both (Patel et al, 2007). Here, we outline the differences between these characteristics and will attempt to address their convergent properties later on.…”