Importin β contains a COOH-terminal nucleoporin binding region important for nuclear transport

Proteins containing a classical NLS are transported into the nucleus by the import receptor importin β, which binds to cargoes via the adaptor importin α. The import complex is translocated through the nuclear pore complex by interactions of importin β with a series of nucleoporins. Previous studies have defined a nucleoporin binding region in the NH2-terminal half of importin β. Here we report the identification of a second nucleoporin binding region in its COOH-terminal half. Although the affinity of the COOH-terminal region for nucleoporins is dramatically weaker than that of the NH2-terminal region, sets of mutations that perturb the nucleoporin binding of either region reduce the nuclear import activity of importin β to a similar extent (∼50%). An importin β mutant with a combination of mutations in the NH2- and COOH-terminal regions is completely inactive for nuclear import. Thus, importin β possesses two nucleoporin binding sites, both of which are important for its nuclear import function

Содержание макро- и микроэлементов в волосах у детей с эпилептическими припадками, перенесшими перинатальную патологию центральной нервной системы. Клинико-лабораторные корреляции

Aim of research. Identify the features of the content of trace elements and minerals in hair in children with epileptic seizures that have undergone perinatal pathology of the central nervous system. To determine the specificity of elemental status in patients whose seizures could be stopped, and in patients resistant to pharmacotherapy.Methods. Twenty children with epileptic seizures underwent perinatal pathology of the central nervous system, aged from 3 months to 8 years (an average of 3.04±2.9 years) were controlled. Population is divided into two groups: I group (10 people) - children with epileptic seizures, managed to be stopped. Group II (10 people) - children with epileptic seizures, resistant to therapy. The control group consisted of 10 practically healthy children of the corresponding sex and age. The content of 25 chemical elements: Al, As, Be, Cd, Hg, Li, Ni. Pb, Sn, B, V, I, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, P, Se, Si, Zn, μg / g was determined in hair by atomic-emission spectrometry with inductively coupled argon plasma and mass spectrometry.Results. The children with epileptic seizures showed a statistically significant increase in the content of Ca, Mg, Mn, Pb, a decrease in Sn concentration when comparing the content of elements in the group II and the control group (p <0.05). The increase in the concentration of the toxic element Pb in the group of seriously ill children with pharmacoresistant persisting epileptic seizures is 3.5 times higher than in the control group (p <0.05). The amount of Ca, Mg, Mn, Pb (ƿ from 0.42 to 0.67) in hair directly correlated (according to Spearman) with the severity of the condition and the propensity to resistance to therapy, in feedback - Sn (ƿ -0, 53). The largest number of direct average and strong links with the severity of clinical evidence and the character of structural changes in the brain was noted in Mg.Conclusions. The revealed changes in elemental status may indicate a possible pathogenetic mechanism in the development of clinical symptoms in the patients examined, the formation of pharmaco-resistance to therapy due to a disturbance of the metal-ligand homeostasis. More studies are needed to clarify the importance of the exchange of micro- and macroelements in the development of the diseaseЦелью работы являлось выявление особенностей содержания микро- и макроэлементов в волосах у детей с эпилептическими припадками, перенесших перинатальную патологию центральной нервной системы. По результатам исследования у детей с фармакорезистентными эпилептическими припадками выявлено статистически значимое по сравнению с контролем повышение содержания в волосах Ca, Mg, Mn, Pb, уменьшение концентрации Sn (p<0,05

Influence of cargo size on Ran and energy requirements for nuclear protein import

Previous work has shown that the transport of some small protein cargoes through the nuclear pore complex (NPC) can occur in vitro in the absence of nucleoside triphosphate hydrolysis. We now demonstrate that in the importin α/β and transportin import pathways, efficient in vitro transport of large proteins, in contrast to smaller proteins, requires hydrolyzable GTP and the small GTPase Ran. Morphological and biochemical analysis indicates that the presence of Ran and GTP allows large cargo to efficiently cross central regions of the NPC. We further demonstrate that this function of RanGTP at least partly involves its direct binding to importin β and transportin. We suggest that RanGTP functions in these pathways to promote the transport of large cargo by enhancing the ability of import complexes to traverse diffusionally restricted areas of the NPC

Identification of a Small Molecule Inhibitor of Importin β Mediated Nuclear Import by Confocal On-Bead Screening of Tagged One-Bead One-Compound Libraries

In eukaryotic cells, proteins and RNAs are transported between the nucleus and the cytoplasm by nuclear import and export receptors. Over the past decade, small molecules that inhibit the nuclear export receptor CRM1 have been identified, most notably,leptomycin B. However, up to now no small molecule inhibitors of nuclear import have been described. Here we have used our automated confocal nanoscanning and bead picking method (CONA) for on-bead screening of a one-bead one-compound library to identify the first such import inhibitor, karyostatin 1A. Karyostatin 1A binds importin beta with high nanomolar affinity and specifically inhibits importin alpha/beta mediated nuclear import at low micromolar concentrations in vitro and in living cells, without perturbing transportin mediated nuclear import or CRM1 mediated nuclear export. Surface plasmon resonance binding-experiments suggest that karyostatin 1A acts by disrupting the interaction between importin p and the OPase Ran. As a selective inhibitor of the importin alpha/beta import pathway, karyostatin 1A will provide a valuable tool for future studies of nucleocytoplasmic trafficking.</p

Diversification of importin-α isoforms in cellular trafficking and disease states.

The human genome encodes seven isoforms of importin α which are grouped into three subfamilies known as α1, α2 and α3. All isoforms share a fundamentally conserved architecture that consists of an N-terminal, autoinhibitory, importin-β-binding (IBB) domain and a C-terminal Arm (Armadillo)-core that associates with nuclear localization signal (NLS) cargoes. Despite striking similarity in amino acid sequence and 3D structure, importin-α isoforms display remarkable substrate specificity in vivo. In the present review, we look at key differences among importin-α isoforms and provide a comprehensive inventory of known viral and cellular cargoes that have been shown to associate preferentially with specific isoforms. We illustrate how the diversification of the adaptor importin α into seven isoforms expands the dynamic range and regulatory control of nucleocytoplasmic transport, offering unexpected opportunities for pharmacological intervention. The emerging view of importin α is that of a key signalling molecule, with isoforms that confer preferential nuclear entry and spatiotemporal specificity on viral and cellular cargoes directly linked to human diseases

Scaffold nucleoporins Nup188 and Nup192 share structural and functional properties with nuclear transport receptors

Nucleocytoplasmic transport is mediated by nuclear pore complexes (NPCs) embedded in the nuclear envelope. About 30 different proteins (nucleoporins, nups) arrange around a central eightfold rotational axis to build the modular NPC. Nup188 and Nup192 are related and evolutionary conserved, large nucleoporins that are part of the NPC scaffold. Here we determine the structure of Nup188. The protein folds into an extended stack of helices where an N-terminal 130 kDa segment forms an intricate closed ring, while the C-terminal region is a more regular, superhelical structure. Overall, the structure has distant similarity with flexible S-shaped nuclear transport receptors (NTRs). Intriguingly, like NTRs, both Nup188 and Nup192 specifically bind FG-repeats and are able to translocate through NPCs by facilitated diffusion. This blurs the existing dogma of a clear distinction between stationary nups and soluble NTRs and suggests an evolutionary relationship between the NPC and the soluble nuclear transport machinery.National Center for Research Resources (U.S.) (Award RR-15301)National Institutes of Health (U.S.) (R01GM077537)National Institutes of Health (U.S.) (R01GM058065)Lundbeck FoundationDanish Council for Independent Research (DFF Sapere Aude)National Cancer Institute (U.S.) (U54CA143836

Genome-wide computational identification of WG/GW Argonaute-binding proteins in Arabidopsis

Domains in Arabidopsis proteins NRPE1 and SPT5-like, composed almost exclusively of repeated motifs in which only WG or GW sequences and an overall amino-acid preference are conserved, have been experimentally shown to bind multiple molecules of Argonaute (AGO) protein(s). Domain swapping between the WG/GW domains of NRPE1 and the human protein GW182 showed a conserved function. As classical sequence alignment methods are poorly-adapted to detect such weakly-conserved motifs, we have developed a tool to carry out a systematic analysis to identify genes potentially encoding AGO-binding GW/WG proteins. Here, we describe exhaustive analysis of the Arabidopsis genome for all regions potentially encoding proteins bearing WG/GW motifs and consider the possible role of some of them in AGO-dependent mechanisms. We identified 20 different candidate WG/GW genes, encoding proteins in which the predicted domains range from 92aa to 654aa. These mostly correspond to a limited number of families: RNA-binding proteins, transcription factors, glycine-rich proteins, translation initiation factors and known silencing-associated proteins such as SDE3. Recent studies have argued that the interaction between WG/GW-rich domains and AGO proteins is evolutionarily conserved. Here, we demonstrate by an in silico domain-swapping simulation between plant and mammalian WG/GW proteins that the biased amino-acid composition of the AGO-binding sites is conserved

Components of Coated Vesicles and Nuclear Pore Complexes Share a Common Molecular Architecture

Numerous features distinguish prokaryotes from eukaryotes, chief among which are the distinctive internal membrane systems of eukaryotic cells. These membrane systems form elaborate compartments and vesicular trafficking pathways, and sequester the chromatin within the nuclear envelope. The nuclear pore complex is the portal that specifically mediates macromolecular trafficking across the nuclear envelope. Although it is generally understood that these internal membrane systems evolved from specialized invaginations of the prokaryotic plasma membrane, it is not clear how the nuclear pore complex could have evolved from organisms with no analogous transport system. Here we use computational and biochemical methods to perform a structural analysis of the seven proteins comprising the yNup84/vNup107–160 subcomplex, a core building block of the nuclear pore complex. Our analysis indicates that all seven proteins contain either a β-propeller fold, an α-solenoid fold, or a distinctive arrangement of both, revealing close similarities between the structures comprising the yNup84/vNup107–160 subcomplex and those comprising the major types of vesicle coating complexes that maintain vesicular trafficking pathways. These similarities suggest a common evolutionary origin for nuclear pore complexes and coated vesicles in an early membrane-curving module that led to the formation of the internal membrane systems in modern eukaryotes

Karyopherins regulate nuclear pore complex barrier and transport function

Nucleocytoplasmic transport is sustained by karyopherins (Kaps) and a Ran guanosine triphosphate (RanGTP) gradient that imports nuclear localization signal (NLS)–specific cargoes (NLS-cargoes) into the nucleus. However, how nuclear pore complex (NPC) barrier selectivity, Kap traffic, and NLS-cargo release are systematically linked and simultaneously regulated remains incoherent. In this study, we show that Kap α facilitates Kap β 1 turnover and occupancy at the NPC in a RanGTP-dependent manner that is directly coupled to NLS-cargo release and NPC barrier function. This is underpinned by the binding affinity of Kap β 1 to phenylalanine–glycine nucleoporins (FG Nups), which is comparable with RanGTP·Kap β 1, but stronger for Kap α ·Kap β 1. On this basis, RanGTP is ineffective at releasing standalone Kap β 1 from NPCs. Depleting Kap α ·Kap β 1 by RanGTP further abrogates NPC barrier function, whereas adding back Kap β 1 rescues it while Kap β 1 turnover softens it. Therefore, the FG Nups are necessary but insufficient for NPC barrier function. We conclude that Kaps constitute integral constituents of the NPC whose barrier, transport, and cargo release functionalities establish a continuum under a mechanism of Kap-centric control

Functional specialization of Piwi proteins in Paramecium tetraurelia from post-transcriptional gene silencing to genome remodelling

Proteins of the Argonaute family are small RNA carriers that guide regulatory complexes to their targets. The family comprises two major subclades. Members of the Ago subclade, which are present in most eukaryotic phyla, bind different classes of small RNAs and regulate gene expression at both transcriptional and post-transcriptional levels. Piwi subclade members appear to have been lost in plants and fungi and were mostly studied in metazoa, where they bind piRNAs and have essential roles in sexual reproduction. Their presence in ciliates, unicellular organisms harbouring both germline micronuclei and somatic macronuclei, offers an interesting perspective on the evolution of their functions. Here, we report phylogenetic and functional analyses of the 15 Piwi genes from Paramecium tetraurelia. We show that four constitutively expressed proteins are involved in siRNA pathways that mediate gene silencing throughout the life cycle. Two other proteins, specifically expressed during meiosis, are required for accumulation of scnRNAs during sexual reproduction and for programmed genome rearrangements during development of the somatic macronucleus. Our results indicate that Paramecium Piwi proteins have evolved to perform both vegetative and sexual functions through mechanisms ranging from post-transcriptional mRNA cleavage to epigenetic regulation of genome rearrangements