Cargo surface hydrophobicity is sufficient to overcome the nuclear pore complex selectivity barrier

Abstract

To fulfil their function, nuclear pore complexes (NPCs) must discriminate between inert proteins and nuclear transport receptors (NTRs), admitting only the latter. This specific permeation is thought to depend on interactions between hydrophobic patches on NTRs and phenylalanine-glycine (FG) or related repeats that line the NPC. Here, we tested this premise directly by conjugating different hydrophobic amino-acid analogues to the surface of an inert protein and examining its ability to cross NPCs unassisted by NTRs. Conjugation of as few as four hydrophobic moieties was sufficient to enable passage of the protein through NPCs. Transport of the modified protein proceeded with rates comparable to those measured for the innate protein when bound to an NTR and was relatively insensitive both to the nature and density of the amino acids used to confer hydrophobicity. The latter observation suggests a non-specific, small, and pliant interaction network between cargo and FG repeats.

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

“…Likewise, NTF2 44 as well as non-specific molecules that exert sufficient FG-repeat binding 63,64 might exhibit varying degrees of ROD-like translocation.…”

Karyopherin-independent spontaneous transport of amphiphilic proteins through the nuclear pore

“…Such protein classes often contain amphiphilic helices and include: i) cytoskeletal proteins containing spectrin repeats (Kumeta et al, 2010); ii) nuclear shuttling/signaling molecules containing armadillo repeats (Yokoya et al, 1999); and iii) a group of proteins containing HEAT repeats, to which, interestingly, the karyopherins themselves belong. Recently, it was revealed through the use of chemically modified BSA that molecular surface hydrophobicity is sufficient to overcome the selectivity barrier of the NPC (Naim et al, 2009). In this study, we focused on the amphiphilic nature of certain proteins and found that they undergo a conformational change to adapt to a hydrophobic environment, with a resulting increase in surface hydrophobicity facilitating spontaneous passage through the NPC.…”

A Bimodal Distribution of Two Distinct Categories of Intrinsically Disordered Structures with Separate Functions in FG Nucleoporins

“…Indeed, the selective properties of the NPC toward kaps have been reconstituted in vitro using isolated FG domains on beads (27,28), FG domain hydrogels (29), and FG domains attached to holes in membranes (30), highlighting the inherent capability of these domains to form selective diffusion barriers that can be specifically permeated by kaps. The exact configuration of FG domains within the NPC and the mechanism of kap movement across the NPC are the subject of much speculation (31), but it seems clear that kaps and passing macromolecules must overcome a hydrophobic barrier imposed by FG domains (24,32,33).…”