Structural and functional analysis of Nup133 domains reveals modular building blocks of the nuclear pore complex

Nucleocytoplasmic transport occurs through nuclear pore complexes (NPCs) whose complex architecture is generated from a set of only ∼30 proteins, termed nucleoporins. Here, we explore the domain structure of Nup133, a nucleoporin in a conserved NPC subcomplex that is crucial for NPC biogenesis and is believed to form part of the NPC scaffold. We show that human Nup133 contains two domains: a COOH-terminal domain responsible for its interaction with its subcomplex through Nup107; and an NH₂-terminal domain whose crystal structure reveals a seven-bladed β-propeller. The surface properties and conservation of the Nup133 β-propeller suggest it may mediate multiple interactions with other proteins. Other β-propellers are predicted in a third of all nucleoporins. These and several other repeat-based motifs appear to be major elements of nucleoporins, indicating a level of structural repetition that may conceptually simplify the assembly and disassembly of this huge protein complex.