Architecture of the Xenopus nuclear pore complex revealed by three-dimensional cryo-electron microscopy.
The nuclear pore complex spans the nuclear envelope and functions as a macromolecular transporter in the ATP-dependent process of nucleocytoplasmic transport. In this report, we present three dimensional (3D) structures for both membrane-associated and detergent-extracted Xenopus NPCs, imaged in frozen buffers by cryo-electron microscopy. A comparison of the differing configurations present in the 3D maps suggests that the spokes may possess an intrinsic conformational flexibility. When combined with recent data from a 3D map of negatively stained NPCs (Hinshaw, J. E., B. O. Carragher, and R. A. Milligan. 1992. Cell. 69:1133-1141), these observations suggest a minimal domain model for the spoke-ring complex which may account for the observed plasticity of this assembly. Moreover, lumenal domains in adjacent spokes are interconnected by radial arm dimers, forming a lumenal ring that may be responsible for anchoring the NPC within the nuclear envelope pore. Importantly, the NPC transporter is visualized as a centrally tapered cylinder that spans the entire width of the NPC, in a direction normal to the nuclear envelope. The central positioning, tripartite structure, and hollow nature of the transporter suggests that it may form a macromolecular transport channel, with a globular gating domain at each end. Finally, the packing of the transporter within the spokes creates a set of eight internal channels that may be responsible, in part, for the diffusion of ions and small molecules across the nuclear envelope.
Akey
C W
CW
Department of Biophysics, Boston University School of Medicine, Massachusetts 02118-2394.
Radermacher
M
M
D000818:Animals; D001693:Biological Transport, Active; D003902:Detergents; D005260:Female; D005615:Freezing; D008854:Microscopy, Electron; D008961:Models, Structural; D009685:Nuclear Envelope / Q000648:ultrastructure*; D009865:Oocytes / Q000648:ultrastructure*; D011487:Protein Conformation; D014981:Xenopus
D003902:Detergents