The property of this ‘selective permeability barrier’ of NPC is presumably attributed to either the highly dense unfolded FG domains which function as entropic bristles for macromolecules ( Rout et al., 2003 Lim et al., 2006) which also can be collapsed upon karyopherin binding ( Lim et al., 2007) or the formation of cohesive meshwork through self- or inter-FG-Nup interaction ( Ribbeck and Gorlich, 2001 Alber et al., 2007) or hybrid of them ( Patel et al., 2007 Yamada et al., 2010). Thus, FG-Nups are important for selective translocation of transport factor–cargo complexes through the NPC. Indeed, nanotube coated with FG-Nups can selectively allow the transport of karyopherin or karyopherin-cargo complexes ( Jovanovic-Talisman et al., 2009) moreover, some of these FG-Nups can form hydrogels in vitro that selectively allow the influx of transport factors ( Frey and Gorlich, 2007 Hulsmann et al., 2012). Furthermore, FG-Nups can bind to nuclear transport factors ( Radu et al., 1995 Rexach and Blobel, 1995 Hu et al., 1996 Clarkson et al., 1996 Bayliss et al., 2000), which is important for the active transport process of selected molecules. Most of these FG repeats are further classified into either Phe-Gly (FG), Gly-Leu-Phe-Gly (GLFG), or Phe-any-Phe-Gly (FXFG) ( Rout and Wente, 1994).įG-Nups located in the central channel of NPC (central FG-Nups) are important for barrier formation, which inhibits the passive diffusion of macromolecules through the NPC. These FG repeats are found in approximately one-third of Nups (also called as FG-Nups), mostly belonging to the peripheral Nups. One characteristic sequence motif/structural folds of Nups is the tandem repeats of phenylalanine-glycine (FG repeats), which are unfolded in native protein ( Denning et al., 2003).
An example of Nup-classification is (1) membrane Nups, (2) scaffold Nups, and (3) peripheral Nups.
Nups can be classified according to their sequence motifs, structural folds, mobility, or relative localization within the NPC ( Rout et al., 2000 Tran and Wente, 2006 Hoelz et al., 2011 Grossman et al., 2012). Yoneda, in Encyclopedia of Cell Biology, 2016 Nucleoporins (Nups)
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