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Abstract:
The permeability barrier of nuclear pore complexes (NPCs)
controls all exchange of macromolecules between the cytoplasm and the cell
nucleus. It consists of phenylalanine−glycine (FG) repeat domains apparently
organized as an FG hydrogel. It has previously been demonstrated that an FG
hydrogel derived from the yeast nucleoporin Nsp1p reproduces the selectivity of
authentic NPCs. Here we combined time-resolved optical spectroscopy and X-ray
scattering techniques to characterize such a gel. The data suggest a hierarchy of
structures that form during gelation at the expense of unstructured elements. On
the largest scale, protein-rich domains with a correlation length of ∼16.5 nm are
evident. On a smaller length scale, aqueous channels with an average diameter of
∼3 nm have been found, which possibly represent the physical structures
accounting for the passive sieving effect of nuclear pores. The protein-rich
domains contain characteristic β-structures with typical inter-β-strand and inter-
β-sheet distances of 1.3 and 0.47 nm, respectively. During gelation, the formation of oligomeric associates is accompanied by the
transfer of phenylalanines into a hydrophobic microenvironment, supporting the view that this process is driven by a
hydrophobic collapse.
