Dynamic molecular mechanism of the nuclear pore complex permeability barrier.

Nuclear pore complexes (NPCs) mediate nucleocytoplasmic transport of specific macromolecules while impeding the exchange of unsolicited material. However, key aspects of this gating mechanism remain controversial. To address this issue, we determined the nanoscopic behavior of the permeability barrier directly within yeast NPCs at transport-relevant timescales.

Nuclear Pore Membrane Proteins Self-Assemble into Nanopores.

Large multiprotein nanopores remain difficult to reconstitute in vitro, such as, for instance, the nuclear pore complex (NPC) that regulates macromolecular transport between the nucleus and cytoplasm in cells. Here, we report that two NPC pore membrane proteins self-assemble into ∼20 nm diameter nanopores following in vitro reconstitution into lipid bilayers. Pore formation follows from the assembly of Pom121 and Ndc1 oligomers, which arrange into ringlike membrane structures that encircle aqueous, electrically conductive pores.

Structural dynamics of the nuclear pore complex.

Nuclear pore complexes (NPCs) are the sole conduits that facilitate macromolecular exchange between the nucleus and cytosol. Recent advancements have led to a more highly resolved NPC structure. However, our understanding of the NPC modus operandi that facilitates transport selectivity, and speed, of diverse cargoes remains incomplete.

Switching head group selectivity in mammalian sphingolipid biosynthesis by active-site-engineering of sphingomyelin synthases.

SM is a fundamental component of mammalian cell membranes that contributes to mechanical stability, signaling, and sorting. Its production involves the transfer of phosphocholine from phosphatidylcholine onto ceramide, a reaction catalyzed by SM synthase (SMS)1 in the Golgi and SMS2 at the plasma membrane. Mammalian cells also synthesize trace amounts of the SM analog, ceramide phosphoethanolamine (CPE), but the physiological relevance of CPE production is unclear.

Nucleocytoplasmic Transport: A Paradigm for Molecular Logistics in Artificial Systems.

Artificial organelles, molecular factories and nanoreactors are membrane-bound systems envisaged to exhibit cell-like functionality. These constitute liposomes, polymersomes or hybrid lipo-polymersomes that display different membrane-spanning channels and/or enclose molecular modules. To achieve more complex functionality, an artificial organelle should ideally sustain a continuous influx of essential macromolecular modules (i.

Switching head group selectivity in mammalian sphingolipid biosynthesis by active-site engineering of sphingomyelin synthases.

SM is a fundamental component of mammalian cell membranes that contributes to mechanical stability, signaling, and sorting. Its production involves the transfer of phosphocholine from phosphatidylcholine onto ceramide, a reaction catalyzed by SM synthase (SMS) 1 in the Golgi and SMS2 at the plasma membrane. Mammalian cells also synthesize trace amounts of the SM analog ceramide phosphoethanolamine (CPE), but the physiological relevance of CPE production is unclear.

Inner workings and biological impact of phospholipid flippases.

The plasma membrane, trans-Golgi network and endosomal system of eukaryotic cells are populated with flippases that hydrolyze ATP to help establish asymmetric phospholipid distributions across the bilayer. Upholding phospholipid asymmetry is vital to a host of cellular processes, including membrane homeostasis, vesicle biogenesis, cell signaling, morphogenesis and migration. Consequently, defining the identity of flippases and their biological impact has been the subject of intense investigations.

Mapping functional interactions in a heterodimeric phospholipid pump.

Type 4 P-type ATPases (P(4)-ATPases) catalyze phospholipid transport to generate phospholipid asymmetry across membranes of late secretory and endocytic compartments, but their kinship to cation-transporting P-type transporters raised doubts about whether P(4)-ATPases alone are sufficient to mediate flippase activity. P(4)-ATPases form heteromeric complexes with Cdc50 proteins. Studies of the enzymatic properties of purified P(4)-ATPase·Cdc50 complexes showed that catalytic activity depends on direct and specific interactions between Cdc50 subunit and transporter, whereas in vivo interaction assays suggested that the binding affinity for each other fluctuates during the transport reaction cycle.