O-GlcNAc modification of nuclear pore complexes accelerates bidirectional transport

Macromolecular transport across the nuclear envelope depends on facilitated diffusion through nuclear pore complexes (NPCs). The interior of NPCs contains a permeability barrier made of phenylalanine-glycine (FG) repeat domains that selectively facilitates the permeation of cargoes bound to nuclear transport receptors (NTRs). FG-repeat domains in NPCs are a major site of O-linked N-acetylglucosamine (O-GlcNAc) modification, but the functional role of this modification in nucleocytoplasmic transport is unclear. We developed high-throughput assays based on optogenetic probes to quantify the kinetics of nuclear import and export in living human cells. We found that increasing O-GlcNAc modification of the NPC accelerated NTR-facilitated transport of proteins in both directions, and decreasing modification slowed transport. Superresolution imaging revealed strong enrichment of O-GlcNAc at the FG-repeat barrier. O-GlcNAc modification also accelerated passive permeation of a small, inert protein through NPCs. We conclude that O-GlcNAc modification accelerates nucleocytoplasmic transport by enhancing the nonspecific permeability of the FG-repeat barrier, perhaps by steric inhibition of interactions between FG repeats.

A designer FG-Nup that reconstitutes the selective transport barrier of the nuclear pore complex

Nuclear Pore Complexes (NPCs) regulate bidirectional transport between the nucleus and the cytoplasm. Intrinsically disordered FG-Nups line the NPC lumen and form a selective barrier, where transport of most proteins is inhibited whereas specific transporter proteins freely pass. The mechanism underlying selective transport through the NPC is still debated. Here, we reconstitute the selective behaviour of the NPC bottom-up by introducing a rationally designed artificial FG-Nup that mimics natural Nups. Using QCM-D, we measure selective binding of the artificial FG-Nup brushes to the transport receptor Kap95 over cytosolic proteins such as BSA. Solid-state nanopores with the artificial FG-Nups lining their inner walls support fast translocation of Kap95 while blocking BSA, thus demonstrating selectivity. Coarse-grained molecular dynamics simulations highlight the formation of a selective meshwork with densities comparable to native NPCs. Our findings show that simple design rules can recapitulate the selective behaviour of native FG-Nups and demonstrate that no specific spacer sequence nor a spatial segregation of different FG-motif types are needed to create selective NPCs.

EFFECTS OF STATIONARY CONTRACTION OF THE SMALL INTESTINE ON DIGESTION

In this paper, effects of stationary contraction on mixing and transport of a non-Newtonian fluid in the small intestine are analyzed theoretically. A semi-analytical method is developed to solve the governing equations of fluids flow in the intestine using lubrication theory. Results indicate that the stationary contraction helps in conferring two functions – (1) shearing of the contents, and (2) bidirectional transport over a short distance. The flow resulting from contraction is symmetric and occurs in both the directions; however, they do not lead to a net flow rate in one direction. The amount of shearing developed during such flows is reflective of their mixing ability. The effort of such peristalsis is largely determined by the flow behavior index; where energy requirements of developing similar shearing forces are higher for dilatants and lower for pseudoplastics. Flow is sensitive to frequency of contraction, luminal occlusion and wavelength of the contraction.

Structural and thermodynamic analyses of human TMED1 (p24γ1) Golgi dynamics

The transmembrane emp24 domain-containing proteins (TMED), also called p24 proteins, are members of a family of sorting receptors present in all representatives of the domain Eukarya and abundantly present in all subcompartments of the early secretory pathway, namely the endoplasmic reticulum (ER), the Golgi, and the intermediate compartment. Although essential during the bidirectional transport between the ER and the Golgi, there is still a lack of information regarding the TMEDs structure, oligomerization propensity, and biophysics of their interactions with the transport cargo. Here, we describe the first high-resolution structure of the Golgi dynamics (GOLD) domain of a TMED1 representative and its biophysical characterization in solution. The crystal structure showed a dimer formation that is also present in solution in a salt-dependent manner, suggesting that the GOLD domain can form homodimers even in the absence of the TMED1 coiled-coil region. A molecular dynamics description of the dimer stabilization, with a phylogenetic analysis of the residues important for the oligomerization and a model for the orientation towards the lipid membrane are also presented.

Bidirectional, unlike unidirectional transport, allows transporting axonal cargos against their concentration gradient

Even though most axonal cargos are synthesized in the soma, the concentration of many of these cargos is larger at the presynaptic terminal than in the soma. This requires transport of these cargos from the soma to the presynaptic terminal or other active sites in the axon. Axons utilize both bidirectional (for example, slow axonal transport) and unidirectional (for example, fast anterograde axonal transport) modes of cargo transport. Bidirectional transport seems to be less efficient because it requires more time and takes more energy to deliver cargos. In this paper, bidirectional and unidirectional axonal transport processes are investigated with respect to their ability to transport cargos against their concentration gradient. We argue that because bidirectional axonal transport includes both the anterograde and retrograde cargo populations, information about cargo concentration at the axon entrance and at the presynaptic terminal can travel in both anterograde and retrograde directions. This allows bidirectional axonal transport to account for the concentration of cargos at the presynaptic terminal. In unidirectional axonal transport, on the contrary, cargo transport occurs only in one direction, and this disallows transport of information about the cargo concentration at the opposite boundary. For the case of unidirectional anterograde transport, this means that proximal regions of the axon do not receive information about cargo concertation in the distal regions. This does not allow for the imposition of a higher concentration at the presynaptic terminal in comparison to the cargo concentration at the axon hillock. To the best of our knowledge, our paper presents the first explanation for the utilization of seemingly inefficient bidirectional transport in neurons.

Cargo transport through the nuclear pore complex at a glance

ABSTRACTBidirectional transport of macromolecules across the nuclear envelope is a hallmark of eukaryotic cells, in which the genetic material is compartmentalized inside the nucleus. The nuclear pore complex (NPC) is the major gateway to the nucleus and it regulates nucleocytoplasmic transport, which is key to processes including transcriptional regulation and cell cycle control. Accordingly, components of the nuclear transport machinery are often found to be dysregulated or hijacked in diseases. In this Cell Science at a Glance article and accompanying poster, we provide an overview of our current understanding of cargo transport through the NPC, from the basic transport signals and machinery to more emerging aspects, all from a ‘cargo perspective’. Among these, we discuss the transport of large cargoes (>15 nm), as well as the roles of different cargo properties to nuclear transport, from size and number of bound nuclear transport receptors (NTRs), to surface and mechanical properties.

The Intestinal Efflux Transporter Inhibition Activity of Xanthones from Mangosteen Pericarp: An In Silico, In Vitro and Ex Vivo Approach

The capacity of α-mangostin (α-MG) and β-mangostin (β-MG) from mangosteen pericarp on P-glycoprotein (Pgp) in silico, in vitro, and ex vivo was investigated in this study. Screening with the ADMET Predictor™ program predicted the two compounds to be both a Pgp inhibitor and Pgp substrate. The compounds tended to interact with Pgp and inhibit Pgp ATPase activity. Additionally, bidirectional transport on Caco-2 cell monolayers demonstrated a significantly lower efflux ratio than that of the control (α-(44.68) and β-(46.08) MG versus the control (66.26); p < 0.05) indicating an inhibitory effect on Pgp activity. Test compounds additionally revealed a downregulation of MDR1 mRNA expression. Moreover, an ex vivo absorptive transport in everted mouse ileum confirmed the previous results that α-MG had a Pgp affinity inhibitor, leading to an increase in absorption of the Pgp substrate in the serosal side. In conclusion, α- and β-MG have the capability to inhibit Pgp and they also alter Pgp expression, which makes them possible candidates for reducing multidrug resistance. Additionally, they influence the bioavailability and transport of Pgp substrate drugs.