Otto, T. A. | Search bioRxiv

bioRxiv2023

Nucleoporin Nsp1 surveils the phase state of FG-Nups

Transport through the NPC relies on intrinsically disordered FG-Nups forming a selective barrier. Away from the NPC, FG-Nups readily form condensates and aggregates, and we address how this behavior is surveilled in cells. FG-Nups, including Nsp1, together with nuclear transport receptor Kap95, form a native cytosolic condensate in yeast. In aged cells this condensate disappears as cytosolic Nsp1 levels decline. Biochemical assays and modeling show that Nsp1 is a modulator of FG-Nup liquid-liquid phase separation, promoting a liquid-like state. Nsp1s presence in the cytosol and condensates is critical, as a reduction of cytosolic levels in young cells induces NPC assembly and transport defects and a general decline in protein quality control, all quantitatively mimicking aging phenotypes. Excitingly, these phenotypes can be rescued by cytosolic Nsp1. We conclude that Nsp1 is a phase state regulator that surveils FG-Nups and impacts general protein homeostasis. HighlightsO_LINups form native cytosolic condensates C_LIO_LINsp1 reduction mimics NPC aging phenotypes C_LIO_LINsp1 acts as phase state modulator of FG-Nups C_LIO_LINsp1 shares surveillance function with classical chaperones C_LI

cell biology↗

bioRxiv2023

Specificity and mechanism of 1,6 hexanediol-induced disruption of nuclear transport

Selective transport through the nuclear pore complex (NPC) depends on the dynamic binding of the intrinsically disordered components of the NPC, the FG-nups, with each other and with nuclear transport receptors (NTRs). Hydrophobic interactions with the phenylalanines of FG-nups are critical for this dynamic binding. 1,6-hexanediol (1,6HD), is an aliphatic alcohol that interferes with hydrophobic interactions. Here we assessed the specificity and mechanism by which 1,6HD disrupts the permeability barrier of NPCs in live bakers yeast cells. Exposure to 1,6HD (10 min, 0-5%) leads to gradual loss of the NPC permeability. This is likely a direct effect on the nuclear transport machinery as cell viability, the pH and ATP levels in the cytosol, as well as the appearance of mitochondria, Golgi, peroxisomes, ER, vacuoles, plasma membrane, nucleolus, secretory pathway and stress granules are not notably changed. There are however effects on the cytoskeleton and Hsp104 to be noted. While 1,6HD treatment does not lead to dissociation or degradation of NPC subunits, a massive relocation of multiple NTRs from NPCs does occur. This displacement quantitatively correlates with the increased passive permeability of NPCs. The loss of NTRs and associated cargo will present a major change in the macromolecular crowding and composition and hence the physicochemical properties of the central channel. We conclude that 1,6HD provides a surprisingly specific intervention to temporarily permeate NPCs and we present evidence that the mechanism includes release of NTRs from the NPCs.

molecular biology↗