Cu2‐xS Surface Phases and Their Impact on the Electronic Structure of CuInS2 Thin Films – A Hidden Parameter in Solar Cell Optimization

The surface properties of CuInS₂ (CIS) thin‐film solar cell absorbers are investigated by a combination of electron and soft X‐ray spectroscopies. Spatially separated regions of varying colors are observed and identified to be dominated by either CuS or Cu₂S surface phases. After their removal by KCN etching, the samples cannot be distinguished by eye and the CIS surface is found to be Cu‐deficient in both regions. However, a significantly more pronounced off‐stoichiometry in the region initially covered by Cu₂S can be identified. In this region, the resulting surface band gap is also significantly larger than the E_g^Surf of the initially CuS‐terminated region. Such variations may represent a hidden parameter which, if overlooked, induces irreproducibility and thus prevents systematic optimization efforts.     

Phosphoinositide 3-Kinase C2beta regulates cytoskeletal organization and cell migration via Rac-dependent mechanisms

Receptor-linked class I phosphoinositide 3-kinases (PI3Ks) induce assembly of signal transduction complexes through protein-protein and protein-lipid interactions that mediate cell proliferation, survival, and migration. Although class II PI3Ks have the potential to make the same phosphoinositides as class I PI3Ks, their precise cellular role is currently unclear. In this report, we demonstrate that class II phosphoinositide 3-kinase C2beta (PI3KC2beta) associates with the Eps8/Abi1/Sos1 complex and is recruited to the EGF receptor as part of a multiprotein signaling complex also involving Shc and Grb2. Increased expression of PI3KC2beta stimulated Rac activity in A-431 epidermoid carcinoma cells, resulting in enhanced membrane ruffling and migration speed of the cells. Conversely, expression of dominant negative PI3KC2beta reduced Rac activity, membrane ruffling, and cell migration. Moreover, PI3KC2beta-overexpressing cells were protected from anoikis and displayed enhanced proliferation, independently of Rac function. Taken together, these findings suggest that PI3KC2beta regulates the migration and survival of human tumor cells by distinct molecular mechanisms.     

Crystal structure of Archaeoglobus fulgidus CTP:inositol-1-phosphate cytidylyltransferase, a key enzyme for di-myo-inositol-phosphate synthesis in (hyper)thermophiles

Many Archaea and Bacteria isolated from hot, marine environments accumulate di-myo-inositol-phosphate (DIP), primarily in response to heat stress. The biosynthesis of this compatible solute involves the activation of inositol to CDP-inositol via the action of a recently discovered CTP:inositol-1-phosphate cytidylyltransferase (IPCT) activity. In most cases, IPCT is part of a bifunctional enzyme comprising two domains: a cytoplasmic domain with IPCT activity and a membrane domain catalyzing the synthesis of di-myo-inositol-1,3′-phosphate-1′-phosphate from CDP-inositol and l-myo-inositol phosphate. Herein, we describe the first X-ray structure of the IPCT domain of the bifunctional enzyme from the hyperthermophilic archaeon Archaeoglobus fulgidus DSMZ 7324. The structure of the enzyme in the apo form was solved to a 1.9-Å resolution. The enzyme exhibited apparent K_m values of 0.9 and 0.6 mM for inositol-1-phosphate and CTP, respectively. The optimal temperature for catalysis was in the range 90 to 95°C, and the V_max determined at 90°C was 62.9 μmol · min⁻¹ · mg of protein⁻¹. The structure of IPCT is composed of a central seven-stranded mixed β-sheet, of which six β-strands are parallel, surrounded by six α-helices, a fold reminiscent of the dinucleotide-binding Rossmann fold. The enzyme shares structural homology with other pyrophosphorylases showing the canonical motif G-X-G-T-(R/S)-X₄-P-K. CTP, l-myo-inositol-1-phosphate, and CDP-inositol were docked into the catalytic site, which provided insights into the binding mode and high specificity of the enzyme for CTP. This work is an important step toward the final goal of understanding the full catalytic route for DIP synthesis in the native, bifunctional enzyme.     

Visualisation and Quantitative Analysis of the Rodent Malaria Liver Stage by Real Time Imaging

The quantitative analysis of Plasmodium development in the liver in laboratory animals in cultured cells is hampered by low parasite infection rates and the complicated methods required to monitor intracellular development. As a consequence, this important phase of the parasite''s life cycle has been poorly studied compared to blood stages, for example in screening anti-malarial drugs. Here we report the use of a transgenic P. berghei parasite, PbGFP-Luc_con, expressing the bioluminescent reporter protein luciferase to visualize and quantify parasite development in liver cells both in culture and in live mice using real-time luminescence imaging. The reporter-parasite based quantification in cultured hepatocytes by real-time imaging or using a microplate reader correlates very well with established quantitative RT-PCR methods. For the first time the liver stage of Plasmodium is visualized in whole bodies of live mice and we were able to discriminate as few as 1–5 infected hepatocytes per liver in mice using 2D-imaging and to identify individual infected hepatocytes by 3D-imaging. The analysis of liver infections by whole body imaging shows a good correlation with quantitative RT-PCR analysis of extracted livers. The luminescence-based analysis of the effects of various drugs on in vitro hepatocyte infection shows that this method can effectively be used for in vitro screening of compounds targeting Plasmodium liver stages. Furthermore, by analysing the effect of primaquine and tafenoquine in vivo we demonstrate the applicability of real time imaging to assess parasite drug sensitivity in the liver. The simplicity and speed of quantitative analysis of liver-stage development by real-time imaging compared to the PCR methodologies, as well as the possibility to analyse liver development in live mice without surgery, opens up new possibilities for research on Plasmodium liver infections and for validating the effect of drugs and vaccines on the liver stage of Plasmodium.     

Unpacking the link between family socioeconomic status and civic engagement during the transition to adulthood: Do work values play a role?

We investigated whether the link between family-of-origin socioeconomic status (SES) and civic engagement in young adulthood is mediated by youth’s work values, that is, the desired characteristics of their current or future jobs. We used data from a Finnish study: 2004 (age 16–18, N_T1?=?1,301); 2011 (age 23–25, N_T2?=?1,096); and 2014 (age 25–27, N_T3?=?1,138). A higher family SES in 2004 predicted youth’s higher civic engagement in 2014. A higher family SES also predicted a lower importance of extrinsic job rewards (e.g., good pay) in 2011, but it was unrelated to the importance of intrinsic job rewards (e.g., learning opportunities). Extrinsic work values, in turn, predicted lower civic engagement in 2014, above and beyond sociodemographic and personality characteristics. Intrinsic work values predicted higher civic engagement. Thus, extrinsic, but not intrinsic, work values partly mediated the link between family SES and youth civic engagement.     

Characterization of the human and mouse sphingosine 1-phosphate receptor, S1P5 (Edg-8): structure-activity relationship of sphingosine1-phosphate receptors.

Five G protein-coupled receptors (S1P(1)/Edg-1, S1P(3)/Edg-3, S1P(2)/Edg-5, S1P(4)/Edg-6, and S1P(5)/Edg-8) for the intercellular lipid mediator sphingosine 1-phosphate have been cloned and characterized. We found human and mouse sequences closely related to rat S1P(5) (97% identical amino acids) and report now the characterization of the human and mouse S1P(5) gene products as encoding sphingosine 1-phosphate receptors. When HEK293T cells were cotransfected with S1P(5) and G protein DNAs, prepared membranes showed sphingosine 1-phosphate concentration-dependent increases in [gamma-(35)S]GTP binding (EC(50) = 12.7 nM). The lipid mediator inhibited forskolin-driven rises in cAMP by greater than 80% after introduction of the mouse or human S1P(5) DNAs into rat hepatoma RH7777 cells (IC(50) = 0.22 nM). This response is blocked fully by prior treatment of cultures with pertussis toxin, thus implicating signaling through G(i/o)alpha proteins. Northern blot analysis showed high expression of human S1P(5) mRNA in spleen, corpus collosum, peripheral blood leukocytes, placenta, lung, aorta, and fetal tissues. Mouse S1P(5) mRNA is also expressed in spleen and brain. Finally, we found that one enantiomer of a sphingosine 1-phosphate analogue wherein the 3-hydroxyl and 4,5-olefin are replaced by an amide functionality shows some selectivity as an agonist S1P(1) and S1P(3) vs S1P(2) and S1P(5).