Nuclear pore complex structure

The nuclear envelope is studed with nuclear pore complex structures, one of which is indicated by the arrow in the photo at top. 

Franke, W. W. (1970). On the universality of the nuclear pore complex structure. Z. Zellforsch. Mikrosk. Anat. 105, 405-429. 

Figure 10 Components of the nuclear pore complex. Structures are available from the PDB and EMDB for some of the components of the nuclear core complex. The individual proteins and small subassemblies shown in ribbon representation are from six PDB entries that provide atomic-level information from X-ray (4GQ2, 3UKY, 4FHN, 3TKN, 4GQ1) or nuclear magnetic resonance spectroscopy (2EC1) studies. The three larger subassemblies drawn as surfaces have been analyzed by cryo-electron microscopy (EMD-5152, EMD-1097) or cryo-electron tomography (EMD-1394).

The nucleus is surrounded by the nuclear envelope, which takes on a lumenal structure connected to the endoplasmic reticulum. The transport of proteins into (and out of) the nucleus occurs through the nuclear pore complex (NPC), a large complex composed of more than 100 different proteins (Talcott and Moore, 1999). Because NPC forms an aqueous pore across the two membranes, small proteins less than 9 nm in diameter can pass through it simply by diffusion. However, most of the transports of both proteins and RNAs are mediated by an active transport mechanism. It is now clear that there is heavy traffic through the NPC in both directions. Proteins are not only imported into the nucleus but also actively exported from it as well. There are many reasons for nuclear export. One reason is to send some shuttle proteins back after their import another is for some viral proteins to export their replicated genomes outside the nucleus. 

The nucleus of the eukaryotic cell is separated from the cytoplasm by the double-membrane nuclear envelope, which provides a continuous boundary between the nucleoplasm and the cytoplasm, except where it is penetrated by nuclear pores, each of which is surrounded by a disklike structure, the nuclear pore complex. These pores serve an export-import function for an exchange of materials between the nucleus and the cytosol. This is necessary in eukaryotic... 

The NE is an elaborate structure that can be divided into several distinct sub-domains the nuclear pore complexes (NPCs), the lamin polymer, and a double membrane system consisting of the outer nuclear membrane (ONM), inner nuclear membrane (INM), lumen, and pore membrane (PoM) together with their integral proteins (Figure 1 see colour insert). The ONM is not only continuous with the ER, but is also studded with ribosomes indicating that in addition to being the outermost layer of the nucleus it is also a subcompartment of the ER. How much of its complement of integral membrane proteins is unique from more distal ER... 

In addition to microtubules, we have imaged other cellular structures, such as clathrin-coated pits, actin, nuclear pore complexes, endoplasmic reticulum, and mitochondria with STORM. The STORM imaging concept applies not... 

An illustrative example of combining protein modeling and electron microscopy data is the case of the apoptosome, an Apaf-1 cytochrome c complex that activates procaspase-9 [40]. The data obtained in this work helped to decipher the exact mechanism of a very important apoptosis triggering mechanism. Another interesting example is the use of computational and biochemical methods to conduct structural analyses of the seven proteins that compose the core building block of the nuclear pore complex [41]. 

The nuclear envelope contains numerous nuclear pore complexes (NPCs), large, complicated structures composed of multiple copies of 50-100 proteins called nucleoporins (see Figure 12-18). FG-nucleoporins, which contain multiple... 

Fig. 10.21. The nuclear pore complex. The approximately 100 different polypeptide chains of the nuclear pore complex form an assembly of 8 spokes attached to two ring structures (a cytoplasmic ring in the outer nuclear membrane and a nuclear ring through the inner membrane) with a transporter plug in the center. Small molecules, ions, and proteins with less than a 50-kDa mass passively diffuse through the pore in either direction. However, RNAs and most proteins are too large to diffuse through, and are actively transported in a process that requires energy, is selective for the molecule transported, is unidirectional, and can be regulated.

Transient PPIs are many and varied. The enumeration of their involvement in so many vital biological functions has reached daunting levels. There are thus many examples, including the recruitment and assembly of the transcription complex, protein transport across membranes, chaperonin-catalyzed protein folding, and the recycling of subcellular structures during the cell cycle. Such recycling includes that of microtubules, the spindle apparatus, the nuclear pore complex, and the nuclear lamina. 

At these points, electron-dense structures termed nuclear pore complexes (Franke, 1970,1974 Aaronson and Blobel, 1974,1975 Maul, 1977) connect the nuclear interior with the cytoplasm. 

Although in higher eukaryotes nuclear pore complexes have not been isolated free of peripheral lamina and other karyoskeletal components, much is currently known about their polypeptide structure. A glycoprotein, gp210 (Gerace et al, 1982 Wozniak et al, 1989 Greber et al, 1990), was the first polypeptide to be identified as a pore complex component by immunoelectron microscopy (Gerace... 

Akey, C. W. (1989). Interactions and structure of the nuclear pore complex revealed by cryo-electron microscopy. J. Cell Biol. 109, 955-970. 

Guam, T., Muller, S., Klier, G., Pante, N., Blevitt, J. M., Haner, M., Paschal, B., Aebi, U., and Gerace, L. (1995). Structural analysis of the p62 complex, an assembly of O-linked glycoproteins that localizes near the central gated channel of the nuclear pore complex. Mol. Biol. Cell 1591-1603. Harris, J. R. (1977). Fractionation of the nuclear envelope. In Methodological Surveys in Biochemistry. Membranous Elements and Movement of Molecules (E. Reid, ed.), Vol. 6, pp. 245-250. Horwood, Chichester. 

Maul, G. G. (1977). The nuclear and the cytoplasmic pore complex Structure, dynamics, distribution, and evolution. Int. Rev. Cytol. Supp. 6, 75-186. 

Pante, N., and Aebi, U. (1995). Toward a molecular understanding of the structure and function of the nuclear pore complex. Int. Rev. Cytol. 162B, 22S-2SS. 

Reichelt, R., Holzenburg, A., Buhle, E. L. Jr., Jamik, M., Engel, A., and Aebi, U. (1990). Correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components. J. Cell BioL 110,883-894. 

The nuclear lamina lies subjacent to the inner nuclear membrane (see Fig. 1 in the chapter by Berrios, this volume) it is a proteinaceous network composed of intermediate filament-like fibrils and is thought to provide structural support to the interphase nucleus. Results of previous studies suggest that the lamina binds specific loci on chromosomes and may thus play a role in organizing the genome within nuclei (Lud rus et al., 1992,1994 Baricheva et al, 19% Zhao et aL, 19% Rzepecki et al., 1997 Sharakhov et al., 1997). Other results suggest that the lamina may also be involved in DNA replication (see, e.g., Moir et al., 1994). The lamina appears to anchor nuclear pore complexes physically. 

Nuclear pore complexes (see Chapter 1, Fig. 1) are morphologically invariant throughout both plant and animal kingdoms. Current results suggest that they regulate both import of specific proteins from cytoplasm to nucleoplasm and export of specific RNA molecules from nucleoplasm to cytoplasm. The structure and function of nuclear pore complexes are considered elsewhere in this volume. 

Fig. 2 Transmission electron micrograph of karyoskeletal protein-enriched fraction prepared from Drosophila embryos. The main panel shows a nucleuslike structure, bounded by a peripheral lamina (L) Inset Higher magnification showing tangential section through the periphery of karyoskeletal protein structure as shown in the main panel. Nuclear pore complex remnants can be readily appreciated as small ringlike structures.

Ris, H. (1991). The three-dimensional structure of the nuclear pore complex as seen by high voltage electron microscopy and high resolution low voltage scanning electron microscopy. EMSA Bull. 21, 54-56. 

Mehlin, H., Daneholt, B.. and Skoglund, U. (1995). Structural interaction between the nuclear pore complex and a specific translocating RNP particle. J. Cell Biol 129, 1205-1216. 

Goldberg, M. W., and Allen, T. D, (1996). The nuclear pore complex and lamina Three dimensional structures and interactions determined by field emission in lens scanning EM. J. Mol. Biol. 257, 848-865. 

Goldberg, M. W., Wiese, C., Allen, T. D., and Wilson, K. L. (1997). Dimples, pores, star rings and thin rings on growing nuclear envelopes Evidence for structural intermediates in nuclear pore complex assembly. J. Cell. Sci. 110, 409-420. 

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