Host chaperones are recruited in membrane-bound complexes by Plasmodium falciparum.

The ability of malarial parasite to deploy proteins at the surface of infected erythrocytes is well known. After their synthesis within the parasite, the cargo proteins are exported from the parasite and carried across the erythrocyte cytoplasm to be delivered at the erythrocyte surface. Our knowledge about the mechanisms involved in this complex trafficking path is limited. We have addressed the involvement of chaperones in traffic across erythrocyte cytoplasm. Our analyses of the chaperones available to the parasite indicated that none of the reported chaperones of the parasite origin are present in the erythrocyte cytoplasm. The chaperones of the host (Hsp70, Hsp90, Hop60), on the other hand, were readily detected in the erythrocyte cytosol. Hypotonic lysis and detergent solubilization experiments indicated that unlike their soluble nature in normal erythrocytes, host chaperones are recruited in membrane-bound, detergent-resistant complexes in infected cells. The association of host-Hsp70 with detergent-resistant complexes was ATP-dependent. Importantly, host chaperones could be detected in knob-enriched fractions and could be cross-linked to the knob subunit, PfHRP1, in a large complex at the surface of the infected erythrocytes. Our results implicate host chaperones in the assembly of parasite proteins such as knob subunits at the erythrocyte surface.     

Insights into the Mechanism of Ligand Binding to Octopine Dehydrogenase from Pecten maximus by NMR and Crystallography

Octopine dehydrogenase (OcDH) from the adductor muscle of the great scallop, Pecten maximus, catalyzes the NADH dependent, reductive condensation of L-arginine and pyruvate to octopine, NAD⁺, and water during escape swimming and/or subsequent recovery. The structure of OcDH was recently solved and a reaction mechanism was proposed which implied an ordered binding of NADH, L-arginine and finally pyruvate. Here, the order of substrate binding as well as the underlying conformational changes were investigated by NMR confirming the model derived from the crystal structures. Furthermore, the crystal structure of the OcDH/NADH/agmatine complex was determined which suggests a key role of the side chain of L-arginine in protein cataylsis. Thus, the order of substrate binding to OcDH as well as the molecular signals involved in octopine formation can now be described in molecular detail.     

A high-powered replication study finds no effect of starting or stopping hormonal contraceptive use on relationship quality

A number of recent studies have implicated that incongruent use of hormonal contraceptives (HCs) negatively affects various aspects of women's romantic relationships. It has been suggested that women with incongruent HC use (a discrepancy in HC use status between when they first met their current partner and the time of study participation) report less sexual satisfaction and higher jealousy scores compared to women with congruent HC use. A similar effect has also been hypothesized for general relationship satisfaction, and recent findings suggest that the association between HC incongruency and women's general relationship satisfaction is moderated by third-party ratings of facial attractiveness of the women's male partners. Using a large convenience sample (N = 948) of Finnish women, we attempted to replicate previously reported findings but found no support for the HC congruency hypothesis, despite excellent statistical power (≥98.7%) to detect previously reported effect sizes. Instead, after dividing our sample into four groups based on HC congruency/incongruency, we found that the largest differences in jealousy, sexual satisfaction, and relationship satisfaction scores tended to be found between women who were consistent HC users and consistent non-users (i.e., between women with different kinds of congruent HC use). We also detected a significant main effect of current HC use on jealousy. We conclude that HC congruency effects reported in previous studies may have spuriously arisen from unequal distributions of current HC users within congruent and incongruent HC user groups.     

Interactions between Newly Synthesized Glycoproteins, Calnexin and a Network of Resident Chaperones in the Endoplasmic Reticulum

Calnexin is a membrane-bound lectin and a molecular chaperone that binds newly synthesized glycoproteins in the endoplasmic reticulum (ER). To analyze the oligomeric properties of calnexin and calnexin-substrate complexes, sucrose velocity gradient centrifugation and chemical cross-linking were used. After CHAPS solubilization of Chinese Hamster Ovary cells, the unoccupied calnexin behaved as a monomer sedimenting at 3.5 S_20,W. For calnexin-substrate complexes the S-values ranged between 3.5–8 S_20,W, the size increasing with the molecular weight of the substrate. Influenza hemagglutinin, a well-characterized substrate associated with calnexin in complexes that sedimented at 5–5.5 S_20,W. The majority of stable complexes extracted from cells, appeared to contain a single calnexin and a single substrate molecule, with about one third of the calnexin in the cell being unoccupied or present in weak associations. However, when chemical cross-linking was performed in intact cells, the calnexin-substrate complexes and calnexin itself was found to be part of a much larger heterogeneous protein network that included other ER proteins. Pulse-chase analysis of influenza-infected cells combined with chemical cross-linking showed that HA was part of large, heterogeneous, cross-linked entities during the early phases of folding, but no longer after homotrimer assembly. The network of weakly associated resident ER chaperones which included BiP, GRP94, calreticulin, calnexin, and other proteins, may serve as a matrix that binds early folding and assembly intermediates and restricts their exit from the ER.     

Interaction of Newly Synthesized Apolipoprotein B with Calnexin and Calreticulin Requires Glucose Trimming in the Endoplasmic Reticulum

Apolipoprotein B (ApoB) is the only protein component of the low density lipoproteins (LDL) in plasma. It is a glycoprotein with a molecular mass of about 550 kDa (4536 amino acids) containing 16 N-glycans. We have studied the interaction of ApoB with two lectin-like chaperones of the Endoplasmic Reticulum (ER)—Calnexin (CN) and Calreticulin (CR). Using a co-immunoprecipitation approach we observed that newly synthesized ApoB associates with CN and CR. The interaction was transient; within 30–60 min after synthesis bulk of newly formed ApoB dissociated. Using McA Rh7777 cells expressing an N-terminal fragment of ApoB we found that inhibition of glucosidases in the ER prevented the association of CN and CR to newly synthesized ApoB. The results showed that like for association with other glycoprotein substrates, trimming of glucose residues was essential for ApoB binding to CN and CR.     

Project DyAdd: Fatty acids in adult dyslexia, ADHD, and their comorbid combination

In project DyAdd, we compared the fatty acid (FA) profiles of serum phospholipids in adults with attention deficit hyperactivity disorder (ADHD) (n=26), dyslexia (n=36), their comorbid combination (n=9), and healthy controls (n=36). FA proportions were analyzed in a 2×2 design with Bonferroni corrected post hoc comparisons. A questionnaire was used to assess dietary fat quality and use of supplements. Results showed that ADHD and dyslexia were not associated with total saturated FAs, monounsaturated FAs, or n-3 polyunsaturated FAs (PUFAs). However, those with ADHD had elevated proportions of total n-6 PUFAs (including γ-linolenic and adrenic acids) as compared to those without ADHD. Dyslexia was related to a higher proportion of monounsaturated nervonic acid and a higher ratio of n-6/n-3 PUFAs. Among females none of the associations were significant. However in males, all the original associations observed in all subjects remained and ADHD was associated with elevated nervonic acid and n-6/n-3 PUFA ratio like dyslexia. Controlling for poorly diagnosed reading difficulties, education, dietary fat quality, or use of FA supplements did not generally remove the originally observed associations.     

Climate-driven synchrony in seed production of masting deciduous and conifer tree species

Aims Understanding fluctuations in plant reproductive investment can constitute a key challenge in ecology, conservation and management. Masting events of trees (i.e. the intermittent and synchronous production of abundant seeding material) is an extreme example of such fluctuations. Our objective was to establish the degree of spatial and temporal synchrony in common four masting tree species in boreal Finland and account for potential causal drivers of these patterns.Methods We investigated the spatial intraspecific and temporal interspecific fluctuations in annual seed production of four tree species in Finland, silver birch Betula pendula Roth, downy birch Betula pubescens Ehrh., Norway spruce Picea abies (L.) H.Karst. and rowanberry Sorbus aucuparia L. We also tested to see whether variations in seed production were linked to annual weather conditions. Seeding abundance data were derived from tens of stands per species across large spatial scales within Finland during 1979 to 2014 (for rowanberries only 1986 to 2014).Important findings All species showed spatial synchrony in seed production at scales up to 1000 km. Annual estimates of seed production were strongly correlated between species. Spring and summer temperatures explained most variation in crop sizes of tree species with 0-to 2-year time lags, whereas rainfall had relatively little influence. Warm weather during flowering (May temperature) in the flowering year (Year t) and 2 years before (t ?2) were correlated with seed production. However, high May temperatures during the previous year (t^-1) adversely affected seed production. Summer temperatures in Year t^-1 was positively correlated with seed production, likely because this parameter enhances the development of flower primordials, but the effect was negative with a time lag of 2 years. The negative feedback in temperature coefficients is also likely due to patterns of resource allocation, as abundant flowering and seed production in these species is thought to reduce the subsequent initiation of potential new flower buds. Since the most important weather variables also showed spatial correlation up to 1000 km, weather parameters likely explain much of the spatial and temporal synchrony in seed production of these four studied tree species.     

Enucleation: a possible mechanism of cancer cell death

There are few major morphologies of cell death that have been described so far: apoptosis (type I), cell death associated with autophagy (type II), necrosis (type III) and anchorage‐dependent mechanisms—anoikis. Here, we show for the first time a possibly novel mechanism inducing tumour cell death under in vitro conditions—enucleation. We pursued the influence of colloidal suspensions of Fe₃O₄ nanoparticles on tumour cell lines (SK‐BR‐3 and MCF‐7 breast cancer cell lines) grown according to standard cell culture protocols. Magnetite nanoparticles were prepared by combustion synthesis and double layer coated with oleic acid. Scanning and transmission electron microscopy revealed that tumour cells developed a network of intracytoplasmic stress fibres, which induce extrusion of nuclei, and enucleated cells die. Normal adult mesenchymal stem cells, used as control, did not exhibit the same behaviour. Intact nuclei were found in culture supernatant of tumour cells, and were visualized by immunofluorescence. Enucleation as a potential mechanism of tumour cell death might open new horizons in cancer biology research and development of therapeutic agents capable of exploiting this behaviour.