A Saturated FG-Repeat Hydrogel Can Reproduce the Permeability Properties of Nuclear Pore Complexes

The permeability barrier of nuclear pore complexes (NPCs) controls the exchange between nucleus and cytoplasm. It suppresses the flux of inert macromolecules ≥ 30 kDa but allows rapid passage of even very large cargoes, provided these are bound to appropriate nuclear transport receptors. We show here that a saturated hydrogel formed by a single nucleoporin FG-repeat domain is sufficient to reproduce the permeability properties of NPCs. Importin β and related nuclear transport receptors entered such hydrogel >1000× faster than a similarly sized inert macromolecule. The FG-hydrogel even reproduced import signal-dependent and importin-mediated cargo influx, allowing importin β to accelerate the gel entry of a large cognate cargo more than 20,000-fold. Intragel diffusion of the importin β-cargo complex occurred rapidly enough to traverse an NPC within ≈12 ms. We extend the “selective phase model” to explain these effects.