The mammalian nuclear pore complex (NPC) conducts nucleocytoplasmic transport and contains multiple copies of nucleoporins (nups). This is the C-terminal interacting domain found on Nup54. Nup45 is a splice variant of Nup58 with an identical α-helical region. Nup54 along with Nup62 and Nup58 are essential for nuclear transport. The C-terminal part of the α-helical region of Nup54 interacts with a C-terminal part of the α-helical region of Nup58. Interestingly, this region appears in two distinct conformations: a single helix and a helix-loop-helix, termed 'straight' and 'bent'. Whereas the straight conformer consists of a 34 residues long alpha helix (residues 460-493), the bent conformer is composed of two alpha helices, each 13 residues long, connected by a central loop (N helix, residues 460-472; C helix, residues 477-489) [].
This entry represents the α-helical domain of human Nup54. Nup54 interacts with Nup58 via the C-terminal part of this domain and Nup62 via the N-terminal part to form the nucleoporin complex []. Nup54, Nup58 and Nup62 all have similar affinities for importin-beta. It seems likely that they are the only FG-repeat nucleoporins of the central channel, and as such they would form a zone of equal affinity spanning the central channel. The diffusion of importin-beta import complexes through the central channel may be a stochastic process as the affinities are similar, whereas movement from cytoplasmic fibrils to the central channel and from the central channel to the nuclear basket would be facilitated by the subtle differences in affinity between them [, ]. In yeast, Nup54 is known as Nup57.
Nucleoporin proteins p58 and p45 are components of the p62 complex, an assembly of four O-linked glycoproteins localised near the central gated channel of the nuclear pore complex, a complex required for the trafficking across the nuclear membrane []. The p45 and p58 isoforms are generated by mRNA alternative splicing []. This entry also includes Nup58 protein from Drosophila melanogaster and Nup45 from Schizosaccharomyces pombe [].
