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 alpha-helical region. Nup54 along with Nup62 and Nup58 are essential for nuclear transport. The C-terminal part of the alpha-helical region of Nup54 interacts with a C-terminal part of the alpha-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) [1].

1: Molecular architecture of the transport channel of the nuclear pore complex. Solmaz SR, Chauhan R, Blobel G, Melcak I; Cell. 2011;147:590-602. PMID:22036567

2: Ring cycle for dilating and constricting the nuclear pore. Solmaz SR, Blobel G, Melcak I; Proc Natl Acad Sci U S A. 2013;110:5858-5863. PMID:23479651