Bound-state mobility within the nuclear pore complex

Biopolymeric filters are essential to life. Nuclear transport in particular is an unusual form of filtering in which the flux of select large particles is greatly enhanced over that of smaller nonspecific molecules. The nuclear pore complex, a channel lined with intrinsically disordered FG nucleoporins, facilitates all transport between the nucleus and cytoplasm. It prevents most macromolecules from crossing the nuclear envelope while allowing the passage of transport factors and their cargo. While the basic biochemical interactions leading to transport are well-understood, the detailed mechanism remains a topic of significant debate. We have developed a model of nuclear transport which predicts that nuclear pore selectivity is largely determined by the mobility of FG nucleoporin–transport factor complexes within the pore. We test this prediction by measuring bound-state diffusion of transport factors in tunable nuclear pore mimics which consist of hydrogels filled with FG nucleoporins. Bound-state diffusion is determined for several conditions, including FG nucleoporins of varying length. Bound-state mobility occurs in many biological systems in addition to the nuclear pore complex and could help explain the selectivity of other biopolymeric filters.