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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The Plasmodium falciparum exported protein PF3D7_0402000 binds to erythrocyte ankyrin and band 4.1

Plasmodium proteins are exported to the erythrocyte cytoplasm to create an environment that supports parasite replication. Although hundreds of proteins are predicted to be exported through PEXEL-dependent and -independent mechanisms, the functions of exported proteins are largely uncharacterized. In this study, we used a biochemical screening approach to identify exported P. falciparum proteins that bound to inside-out vesicles prepared from erythrocytes. Out of 70 exported P. falciparum proteins tested, 18 bound to IOVs in 2 or more independent assays. Using co-affinity purifications followed by mass spectrometry, pairwise co-purification experiments and the split-luciferase assay, we identified 31 putative protein-protein interactions between erythrocyte cytoskeletal proteins and exported P. falciparum proteins. We further showed that PF3D7_1401600 binds to the spectrin-binding domain of erythrocyte ankyrin via its MESA erythrocyte cytoskeleton binding (MEC) motif and to the N-terminal domains of ankyrin and 4.1R through a fragment that required an intact PHIST domain. Introduction of PF3D7_1401600 into erythrocyte ghosts increased retention in the microsphiltration assay, consistent with previous data that reported a reduction of rigidity in red blood cells infected with PF3D7_1401600-deficient parasites. Finally, we found that PfEPF3 proteins bound to erythrocyte GAPDH, providing a potential link between Maurer’s clefts and the erythrocyte cytoskeleton early during infection.

Shakya, Bikash↗
DOE OSTI2015

Nuclear export of cutaneous HPV8 E7 oncoprotein is mediated by a leucine-rich nuclear export signal via a CRM1 pathway

We recently determined that the nuclear import of cutaneous beta genus HPV8 E7 oncoprotein it is mediated by its zinc-binding domain via direct hydrophobic interactions with the FG nucleoporins Nup62 and Nup153 (Onder and Moroianu, 2014). Here we investigated the nuclear export of HPV8 E7 oncoprotein using confocal microscopy after transfections of HeLa cells with EGFP–8cE7 and mutant plasmids and treatment with Ratjadone A nuclear export inhibitor. We determined that HPV8 E7 contains a leucine-rich nuclear export signal (NES), {sub 76}IRTFQELLF{sub 84}, within its zinc-binding domain that mediates its nuclear export via a CRM1 pathway. We found that HPV8 E7 interacts with CRM1 and that the hydrophobic amino acid residues I76, F79 and L82 of the NES are essential for this interaction and for nuclear export of HPV8 E7 oncoprotein. - Highlights: • HPV8 E7 has a leucine-rich NES within its zinc-binding domain that mediates its nuclear export. • CRM1 nuclear export receptor interacts with HPV8 E7 and mediates its export. • Identification of the critical hydrophobic amino acids of the NES of HPV8 E7.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Inhibition of CRM1-mediated nuclear export of influenza A nucleoprotein and nuclear export protein as a novel target for antiviral drug development

An anti-influenza compound, DP2392-E10 based on inhibition of the nuclear export function of the viral nucleoprotein-nuclear export signal 3 (NP-NES3) domain was successfully identified by our previous high-throughput screening system. Here, we demonstrated that DP2392-E10 exerts its antiviral effect by inhibiting replication of a broad range of influenza A subtypes. In regard to the molecular mechanism, we revealed that DP2392-E10 inhibits nuclear export of both viral NP and nuclear export protein (NEP). More specifically, in vitro pull-down assays revealed that DP2392-E10 directly binds cellular CRM1, which mediates nuclear export of NP and NEP. In silico docking suggested that DP2392-E10 binds at a region close to the HEAT9 and HEAT10 domains of CRM1. Together, these results indicate that the CRM1-mediated nuclear export function of influenza virus represents a new potential target for antiviral drug development, and also provide a core structure for a novel class of inhibitors that target this function. - Highlights: •DP2392-E10 inhibits replication of a broad range of influenza A subtypes. •DP2392-E10 inhibits nuclear exports of NP and NEP via their NP-NES3 and NEP-NES2 domains, respectively. •DP2392-E10 is predicted to directly bind CRM1 in the region near the HEAT9 and HEAT10 repeats.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Thiol-facilitated cell export and desorption of methylmercury by anaerobic bacteria

Neurotoxic methylmercury (MeHg), formed by anaerobic bacteria, is shown to be rapidly excreted from the cell, but the mechanism of this process is unclear. Using both Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132 strains, we investigated the factors affecting export and distribution of MeHg in mercury methylation and MeHg sorption-desorption assays. Thiols, such as cysteine, were found to greatly facilitate desorption and export of MeHg, particularly by PCA cells. However, in cysteine-free assays (4 h) >90% of the synthesized MeHg was associated with PCA, among which ~73% was sorbed on the cell surface and 19% remained inside the cells. In comparison, a majority of the MeHg (70%) was exported by ND132, leaving ~20% of the MeHg sorbed on the surface and 10% inside the cells. When MeHg was added directly to the cell suspensions, ND132 adsorbed much lower MeHg but took up more MeHg inside cells than PCA did. These results demonstrate that MeHg export is bacteria strain-specific, time dependent, and is influenced by thiols, implicating important roles of ligand complexation in facilitating MeHg production and mobilization in the environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Structural determinants of nuclear export signal orientation in binding to exportin CRM1

The Chromosome Region of Maintenance 1 (CRM1) protein mediates nuclear export of hundreds of proteins through recognition of their nuclear export signals (NESs), which are highly variable in sequence and structure. The plasticity of the CRM1-NES interaction is not well understood, as there are many NES sequences that seem incompatible with structures of the NES-bound CRM1 groove. Crystal structures of CRM1 bound to two different NESs with unusual sequences showed the NES peptides binding the CRM1 groove in the opposite orientation (minus) to that of previously studied NESs (plus). A comparison of minus and plus NESs identified structural and sequence determinants for NES orientation. The binding of NESs to CRM1 in both orientations results in a large expansion in NES consensus patterns and therefore a corresponding expansion of potential NESs in the proteome.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Nuclear export receptor CRM1 recognizes diverse conformations in nuclear export signals

Nuclear export receptor CRM1 binds highly variable nuclear export signals (NESs) in hundreds of different cargoes. Previously we have shown that CRM1 binds NESs in both polypeptide orientations. Here, we show crystal structures of CRM1 bound to eight additional NESs which reveal diverse conformations that range from loop-like to all-helix, which occupy different extents of the invariant NES-binding groove. Analysis of all NES structures show 5-6 distinct backbone conformations where the only conserved secondary structural element is one turn of helix that binds the central portion of the CRM1 groove. All NESs also participate in main chain hydrogen bonding with human CRM1 Lys568 side chain, which acts as a specificity filter that prevents binding of non-NES peptides. The large conformational range of NES backbones explains the lack of a fixed pattern for its 3-5 hydrophobic anchor residues, which in turn explains the large array of peptide sequences that can function as NESs.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Silicate deposition during decomposition of cyanobacteria may promote export of picophytoplankton to the deep ocean

Marine particles transport organic matter through the water column to the sediment where the organic matter can be buried. This pathway is one of the few natural removal mechanisms of CO 2 from the atmosphere over geological time. Picophytoplankton, major primary producers in the ocean, have until recently been thought unimportant regarding particle transport. Here we provide evidence that silicate is deposited on extracellular polymeric substance (EPS) associated with decomposing picophytoplankton. We also find that Si is enriched in a previously unexplored group of marine particles (called micro-blebs) from the deep-water column. The surprising similarity in morphology and composition between EPS-Si and micro-blebs suggests that EPS-Si may be a precursor of micro-blebs observed in the deep ocean. Finally, this previously unexplored source of silicon may be important to silicon cycling and may further enhance export of picophytoplankton to the deep ocean.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Improving bamboo’s fuel and storage properties with a net energy export through torrefaction paired with catalytic oxidation

Using torrefied char, or biocoal, as solid fuel provides an opportunity to introduce a sustainable feedstock into the energy market. The goals of this study were to investigate how torrefaction improves the energy content and the grindability of a Malaysian bamboo along with understanding the potential for integrated energy recovery from torrefaction gases. The feedstock was torrefied at 250–290 °C for 1 h and the combustion characteristics and grindability of the solid products along with the composition of torrefied gas species were measured. The results showed a beneficial increase in elemental carbon increased from 47 to 63 wt% at 290 °C torrefaction, reflecting an increase in higher heating value from 17.8 to 25.6 MJ/kg. The combustion behavior of all the products appeared to show three distinct combustion zones; however, torrefaction severity leading to higher combustion temperature and time as the fixed carbon augmented with the increase of torrefaction temperature. This increase in severity also lead to more friable and grindable material, and the 290 °C condition required a factor of 2.7 less hold-up time in the mill compared to the raw bamboo, and a factor of 8.5 less energy (938 and 111 kWh/tonne respectively). Through analysis of the gas and volatile formation, a case study showed that catalytic oxidation can convert nearly 100% of the embodied chemical energy into usable thermal energy. These experimental findings were scaled to a 100,000 tonne/y capacity torrefaction plant and in the moderate case of 270 °C operating temperature, the plant has 1.25 GJ/tonne excess energy beyond what the process needs.

09 BIOMASS FUELS↗
DOE OSTI2021

Identifying Key Environmental Factors Explaining Temporal Patterns of DOC Export From Watersheds in the Conterminous United States

The export of dissolved organic carbon (DOC) from a watershed is a key component of the terrestrial biosphere carbon cycle. There is a need to improve our understanding of how and by how much various environmental factors are driving the temporal patterns of DOC export in order to accurately model and evaluate terrestrial carbon storage and fluxes. In this synthesis, we compiled observational data sets from 14 watersheds in the conterminous United States spanning the time period from 1981 to 2017. We used these data sets to examine the relative impacts of various climate, atmospheric deposition, and land cover factors on the temporal patterns of DOC export across watersheds of different sizes and landscape conditions, as well as the time-series autocorrelation of DOC export. Overall, our results suggest that the dominant factor on an annual scale was the amount of precipitation, which had a positive correlation with DOC export from a watershed. Overall increasing nitrogen deposition was coincident with increasing DOC export, and increasing sulfur deposition was coincident with declining DOC export. The seasonal pattern of DOC export was strongly regulated by air temperature, the long-term trend was negatively influenced by increasing sulfur deposition, and no obvious autocorrelation was detected in DOC export. In addition, higher rates of DOC export were positively correlated with greater area of wetlands within a watershed, but was not found to be strongly related to any of the other land cover types.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

“The structure of the Type III secretion system export gate with CdsO, an ATPase lever arm”

Type III protein secretion systems (T3SS) deliver effector proteins from the Gram-negative bacterial cytoplasm into a eukaryotic host cell through a syringe-like, multi-protein nanomachine. Cytosolic components of T3SS include a portion of the export apparatus, which traverses the inner membrane and features the opening of the secretion channel, and the sorting complex for substrate recognition and for providing the energetics required for protein secretion. Two components critical for efficient effector export are the export gate protein and the ATPase, which are proposed to be linked by the central stalk protein of the ATPase. We present the structure of the soluble export gate homo-nonamer, CdsV, in complex with the central stalk protein, CdsO, of its cognate ATPase, both derived from Chlamydia pneumoniae. This structure defines the interface between these essential T3S proteins and reveals that CdsO engages the periphery of the export gate that may allow the ATPase to catalyze an opening between export gate subunits to allow cargo to enter the export apparatus. We also demonstrate through structure-based mutagenesis of the homologous export gate in Pseudomonas aeruginosa that mutation of this interface disrupts effector secretion. These results provide novel insights into the molecular mechanisms governing active substrate recognition and translocation through a T3SS.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Structural basis for influenza virus NS1 protein block of mRNA nuclear export

Influenza viruses antagonize key immune defence mechanisms via the virulence factor non-structural protein 1 (NS1). A key mechanism of virulence by NS1 is blocking nuclear export of host messenger RNAs, including those encoding immune factors; however, the direct cellular target of NS1 and the mechanism of host mRNA export inhibition are not known. Here, we identify the target of NS1 as the mRNA export receptor complex, nuclear RNA export factor 1–nuclear transport factor 2-related export protein 1 (NXF1–NXT1), which is the principal receptor mediating docking and translocation of mRNAs through the nuclear pore complex via interactions with nucleoporins. We determined the crystal structure of NS1 in complex with NXF1–NXT1 at 3.8 Å resolution. The structure reveals that NS1 prevents binding of NXF1–NXT1 to nucleoporins, thereby inhibiting mRNA export through the nuclear pore complex into the cytoplasm for translation. We demonstrate that a mutant influenza virus deficient in binding NXF1–NXT1 does not block host mRNA export and is attenuated. Here, this attenuation is marked by the release of mRNAs encoding immune factors from the nucleus. In sum, our study uncovers the molecular basis of a major nuclear function of influenza NS1 protein that causes potent blockage of host gene expression and contributes to inhibition of host immunity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Mechanisms of Organic Matter Export in Estuaries with Contrasting Carbon Sources

Modifications in land-use and climate will result in shifts in the magnitude and quality of organic matter (OM) transported from wetlands to coastal waters, but differentiation between riverine and wetland OM sources in coastal areas remains a challenge. Here, we evaluate particulate and dissolved OM export dynamics in two representative estuary types—Apalachicola Bay (AP) and Barataria Bay (BB), characterized by primarily blackwater river inputs and high particle abundance, respectively. The magnitude and composition of OM exported from each estuary was evaluated based on seasonal measurements of surface water dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), the stable isotopic composition of DOC and POC (d13C-DOC and d13C-POC, respectively), dissolved and particulate lignin phenols, and carbon-normalized dissolved lignin-phenol yields. Discriminant analyses indicated that BB is a more particle-rich and wetland-carbon dominated system compared to AP, which is due to a lack of direct river inputs and high prevalence of wetlands carbon sources (living vs. eroded/submerged). The primary parameters explaining the predominance of particulate and wetland carbon sources in BB were total suspended sediment concentrations, d13C-DOC, d13C-POC, the ratio of cinnamyl to vanillyl phenols in DOC, and the ratio of syringyl to vanillyl phenols for both POC and DOC. In contrast, AP was separated by DOC, particulate C:N ratios, and the ratio of acid to aldehyde lignin phenols for both POC and DOC, indicating a more terrestrial source of organic matter and reflecting the importance of fluvial DOM inputs in this system. Total lignin export (sum of dissolved and particulate) was higher in BB (5.73×105 kg yr-1) than in AP (4.21×105 kg yr-1). Particulate lignin export from BB was greater than the export of dissolved lignin at either BB or AP, suggesting coastal marsh erosion may be driving this comparatively large export of particulate lignin.

aquatic↗
DOE OSTI2018

Structural–functional interactions of NS1-BP protein with the splicing and mRNA export machineries for viral and host gene expression

The influenza virulence factor NS1 protein interacts with the cellular NS1-BP protein to promote splicing and nuclear export of the viral M mRNAs. The viral M1 mRNA encodes the M1 matrix protein and is alternatively spliced into the M2 mRNA, which is translated into the M2 ion channel. These proteins have key functions in viral trafficking and budding. To uncover the NS1-BP structural and functional activities in splicing and nuclear export, we performed proteomics analysis of nuclear NS1-BP binding partners and showed its interaction with constituents of the splicing and mRNA export machineries. NS1-BP BTB domains form dimers in the crystal. Full-length NS1-BP is a dimer in solution and forms at least a dimer in cells. Mutations suggest that dimerization is important for splicing. The central BACK domain of NS1-BP interacts directly with splicing factors such as hnRNP K and PTBP1 and with the viral NS1 protein. The BACK domain is also the site for interactions with mRNA export factor Aly/REF and is required for viral M mRNA nuclear export. The crystal structure of the C-terminal Kelch domain shows that it forms a β-propeller fold, which is required for the splicing function of NS1-BP. Furthermore, this domain interacts with the polymerase II C-terminal domain and SART1, which are involved in recruitment of splicing factors and spliceosome assembly, respectively. NS1-BP functions are not only critical for processing a subset of viral mRNAs but also impact levels and nuclear export of a subset of cellular mRNAs encoding factors involved in metastasis and immunity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Identification of Exported Plasmodium falciparum Proteins That Bind to the Erythrocyte Cytoskeleton

Plasmodium proteins are exported to the erythrocyte cytoplasm to create an environment that supports parasite replication. Although hundreds of proteins are predicted to be exported through Plasmodium export element (PEXEL)-dependent and -independent mechanisms, the functions of exported proteins are largely uncharacterized. In this study, we used a biochemical screening approach to identify putative exported P. falciparum proteins that bound to inside-out vesicles prepared from erythrocytes. Out of 69 P. falciparum PEXEL-motif proteins tested, 18 bound to inside-out vesicles (IOVs) in two or more independent assays. Using co-affinity purifications followed by mass spectrometry, pairwise co-purification experiments, and the split-luciferase assay, we identified 31 putative protein–protein interactions between erythrocyte cytoskeletal proteins and predicted exported P. falciparum proteins. We further showed that PF3D7_1401600 binds to the spectrin-binding domain of erythrocyte ankyrin via its MESA erythrocyte cytoskeleton binding (MEC) motif and to the N-terminal domains of ankyrin and 4.1R through a fragment that required an intact Plasmodium helical interspersed sub-telomeric (PHIST) domain. Introduction of PF3D7_1401600 into erythrocyte ghosts increased retention in the microsphiltration assay, consistent with previous data that reported a reduction of rigidity in red blood cells infected with PF3D7_1401600-deficient parasites.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Hydrology Outweighs Temperature in Driving Production and Export of Dissolved Carbon in a Snowy Mountain Catchment

Abstract Terrestrial production and export of dissolved organic and inorganic carbon (DOC and DIC) to streams depends on water flow and biogeochemical processes in and beneath soils. Yet, understanding of these processes in a rapidly changing climate is limited. Using the watershed‐scale reactive‐transport model BioRT‐HBV and stream data from a snow‐dominated catchment in the Rockies, we show deeper groundwater flow averaged about 20% of annual discharge, rising to ∼35% in drier years. DOC and DIC production and export peaked during snowmelt and wet years, driven more by hydrology than temperature. DOC was primarily produced in shallow soils (1.94 ± 1.45 gC/m 2 /year), stored via sorption, and flushed out during snowmelt. Some DOC was recharged to and further consumed in the deeper subsurface via respiration (−0.27 ± 0.02 gC/m 2 /year), therefore reducing concentrations in deeper groundwater and stream DOC concentrations at low discharge. Consequently, DOC was primarily exported from the shallow zone (1.62 ± 0.96 gC/m 2 /year, compared to 0.12 ± 0.02 gC/m 2 /year from the deeper zone). DIC was produced in both zones but at higher rates in shallow soils (1.34 ± 1.00 gC/m 2 /year) than in the deep subsurface (0.36 ± 0.02 gC/m 2 /year). Deep respiration elevated DIC concentrations in the deep zone and stream DIC concentrations at low discharge. In other words, deep respiration is responsible for the commonly‐observed increasing DOC concentrations (flushing) and decreasing DIC concentrations (dilution) with increasing discharge. DIC export from the shallow zone was ~66% of annual export but can drop to ∼53% in drier years. Numerical experiments suggest lower carbon production and export in a warmer, drier future, and a higher proportion from deeper flow and respiration processes. These results underscore the often‐overlooked but growing importance of deeper processes in a warming climate.

54 ENVIRONMENTAL SCIENCES↗