Membrane-coating lattice scaffolds in the nuclear pore and vesicle coats: commonalities, differences, challenges - PubMed (original) (raw)

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Membrane-coating lattice scaffolds in the nuclear pore and vesicle coats: commonalities, differences, challenges

Nina C Leksa et al. Nucleus. 2010 Jul-Aug.

Abstract

The nuclear pore complex (NPC) regulates all traffic between the cytoplasm and the nucleus. It is a large protein assembly composed of multiple copies of ∼30 nucleoporins (nups). Structural studies of the NPC have been limited by its considerable size and complexity. Progress toward understanding the structure of this nanomachine has benefited from its modular nature, which allows for this 40-60 MDa assembly to be broken down into subcomplexes that can be studied individually. While recent work by both crystallographers and electron microscopists has greatly enhanced our model of the NPC, the resolution gap between crystal and EM structures remains too large to confidently place individual proteins within the context of the fully assembled NPC. In an effort to arrive at a veritable model of the NPC, we solved the structure of several scaffold nups and defined the ancestral coatomer element (ACE1) common to a set of nucleoporins and COPII vesicle coat proteins. Subsequently, we proposed a lattice-like model of the NPC, analogous to the COPII lattice, in which ACE1 proteins form the edge elements and β-propellers form the vertex elements. Here, we review our recent studies, speculate on how interactions between subcomplexes of the NPC are mediated, and outline the steps and challenges that lay ahead on the path to understanding this enormous assembly in molecular detail.

Keywords: ACE1; assembly; membrane-coating; nuclear pore complex; nucleoporin; ²-propeller.

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Figures

Figure 1

Figure 1

Schematic of ACE1 and the Y-complex. (A) The three modules of the ACE1 domain—crown, trunk and tail—are shown in blue, orange and green, respectively. The positions of the N and C termini are indicated. (B) The relative positions of the nups within the Y complex are shown. ACE1 nups are colored as in (A), all others in gray.

Figure 2

Figure 2

Membrane-coating scaffolds of the NPC and vesicle coats. Schematics of the lattice like assemblies of the NPC and COPII scaffolds are shown, with ACE1 modules colored as in Figure 1. Enlarged views of the ACE1 edge elements are shown for both the NPC and COPII, in addition to the vertex element of the COPII lattice (with Sec31 shown in green and Sec13 shown in gray). The assembly of the vertex element, of the NPC, including which ²-propellers are used, is currently unknown. While the COPII ACE1 interaction is homotypic, the analogous ACE1 interaction between Nup145C and Nup84 is heterotypic. A clathrin triskelion and the entire clathrin coat are shown in the right panel. While the clathrin coat is similarly composed of helical and ²-propeller domains (colored in orange and gray, respectively), overall structure and assembly differ significantly from the NPC and COPII lattices.

Figure 3

Figure 3

Crystal contacts of the Sec13 ²-propeller. A Sec13 reference molecule is shown in orange, with neighboring molecules from five different crystal structures (PDB accession codes 2PM6, 2PM9, 3BG1, 3JRO, 3JRP) superimposed to indicate the number and variety of ²-propeller-²-propeller contacts that the Sec13 molecule can make in the crystal. Neighboring molecules from the same crystal are colored in the same shade of blue.

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