Crystal Structure of the Plasmodium falciparum Thioredoxin Reductase–Thioredoxin Complex

Over the last decades, malaria parasites have been rapidly developing resistance against antimalarial drugs, which underlines the need for novel drug targets. Thioredoxin reductase (TrxR) is crucially involved in redox homeostasis and essential for Plasmodium falciparum. Here, we report the first crystal structure of P. falciparum TrxR bound to its substrate thioredoxin 1. Upon complex formation, the flexible C-terminal arm and an insertion loop of PfTrxR are rearranged, suggesting that the C-terminal arm changes its conformation during catalysis similar to human TrxR. Striking differences between P. falciparum and human TrxR are a Plasmodium-specific insertion and the conformation of the C-terminal arm, which lead to considerable differences in thioredoxin binding and disulfide reduction. Moreover, we functionally analyzed amino acid residues involved in substrate binding and in the architecture of the intersubunit cavity, which is a known binding site for disulfide reductase inhibitors. Cell biological experiments indicate that P. falciparum TrxR is indeed targeted in the parasite by specific inhibitors with antimalarial activity. Differences between P. falciparum and human TrxR and details on substrate reduction and inhibitor binding provide the first solid basis for structure-based drug development and lead optimization.     

Sticholysin I–membrane interaction: An interplay between the presence of sphingomyelin and membrane fluidity

Sticholysin I (St I) is a pore-forming toxin (PFT) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin protein family, a unique class of eukaryotic PFT exclusively found in sea anemones. As for actinoporins, it has been proposed that the presence of sphingomyelin (SM) and the coexistence of lipid phases increase binding to the target membrane. However, little is known about the role of membrane structure and dynamics (phase state, fluidity, presence of lipid domains) on actinoporins' activity or which regions of the membrane are the most favorable platforms for protein insertion. To gain insight into the role of SM on the interaction of St I to lipid membranes we studied their binding to monolayers of phosphatidylcholine (PC) and SM in different proportions. Additionally, the effect of acyl chain length and unsaturation, two features related to membrane fluidity, was evaluated on St I binding to monolayers. This study revealed that St I binds and penetrates preferentially and with a faster kinetic to liquid-expanded films with high lateral mobility and moderately enriched in SM. A high content of SM induces a lower lateral diffusion and/or liquid-condensed phases, which hinder St I binding and penetration to the lipid monolayer. Furthermore, the presence of lipid domain borders does not appear as an important factor for St I binding to the lipid monolayer.     

Plasmodium falciparum RuvB1 is an active DNA helicase and translocates in the 5′–3′ direction

RuvB family of protein contains two similar kinds of proteins i.e. RuvB1 and RuvB2 from yeast to human. These proteins belong to the AAA + class of proteins and are critical components of several multiprotein complexes involved in diverse cellular activities. There are two RuvB proteins annotated in the Plasmodium database but the identification of the third protein recently by our lab has raised the question why Plasmodium falciparum contains three RuvB proteins instead of two. Hence the biochemical characterizations of these proteins have become essential to understand the role of these proteins in the malaria parasite. Recently we have reported the characterization of the recombinant PfRuvB3, which contains ATPase activity but lacks DNA helicase activity. In the present study we report the phylogenetic analysis and detailed biochemical characterization of one of the other RuvB homologue RuvB1 from P. falciparum. PfRuvB1 shows considerable homology with human as well as yeast RuvB1 and contains Walker motif A and Walker motif B. The activity analysis of this protein revealed that PfRuvB1 is an ATPase and this activity increased significantly in the presence of ss-DNA. PfRuvB1 also contains DNA helicase activity and translocates preferentially in 5′ to 3′ direction. In vivo investigation of PfRuvB1 revealed that it is constitutively expressed during all the stages of intraerythrocytic cycle of P. falciparum and localizes mainly to the nucleus. These studies will make important contribution in understanding the role of RuvB protein in P. falciparum.     

Relationship between GSTM1 and GSTT1 polymorphisms and schizophrenia: A case–control study in a Tunisian population

There is substantial evidence found in the literature that supports the fact that the presence of oxidative stress may play an important role in the pathophysiology of schizophrenia. The glutathione S-transferases (GSTs) forms one of the major detoxifying groups of enzymes responsible for eliminating products of oxidative stress. Interindividual differences observed in the metabolism of xenobiotics have been attributed to the genetic polymorphism of genes coding for enzymes involved in detoxification. Thus, in this study we investigated the association of glutathione S-transferase Mu-1 (GSTM1) and glutathione S-transferase theta-1 (GSTT1) gene deletion polymorphisms and schizophrenia in a Tunisian population. A case–control study including 138 schizophrenic patients and 123 healthy controls was enrolled. The GSTM1 and GSTT1 polymorphisms were analyzed by multiplex polymerase chain reaction (PCR). No association was found between the GSTM1 genotype and schizophrenia, whereas the prevalence of the GSTT1 active genotype was significantly higher in the schizophrenic patients (57.2%) than in the controls (45.5%) with (OR = 0.6, IC 0.37–0.99, p = 0.039). Thus, we noted a significant association between schizophrenia and GSTT1 active genotype. Furthermore, the combination of the GSTM1 and GSTT1 null genotypes showed a non-significant trend to an increased risk of schizophrenia. The present finding indicated that GSTT1 seems to be a candidate gene for susceptibility to schizophrenia in at least Tunisian population.     

Complex dynamics of a predator–prey–parasite system: An interplay among infection rate,predator's reproductive gain and preference

Parasites are considered as an important factor in regulating their host populations through trait-mediated effects. On the other hand, predation becomes particularly interesting in host–parasite systems because predation can significantly alter the abundance of parasites and their host population. The combined effects of parasites and predator on host population and community structure therefore may have larger effect. Different field experiments confirm that predators consume disproportionately large number of infected prey in comparison to their susceptible counterpart. There are also substantial evidences that predator has the ability to distinguish prey that have been infected by a parasite and avoid such prey to reduce fitness cost. In this paper we study the predator–prey dynamics, where the prey species is infected by some parasites and predators consume both the susceptible and infected prey with some preference. We demonstrate that complexity in such systems largely depends on the predator's selectivity, force of infection and predator's reproductive gain. If the force of infection and predator's reproductive gain are low, parasites and predators both go to extinction whatever be the predator's preference. The story may be totally different in the opposite case. Survival of species in stable, oscillatory or chaotic states, and their extinction largely depend on the predator's preference. The system may also show two coexistence equilibrium points for some parameter values. The equilibrium with lower susceptible prey density is always stable and the equilibrium with higher susceptible prey density is always unstable. These results suggest that understanding the consequences of predator's selectivity or preference may be crucial for community structure involving parasites.     

O2 and H2O are each the source of one O in NO−2 produced from NH3 by Nitrosomonas: 15N-NMR evidence

The exchange of ¹⁸O between H₂¹⁸O and exogeneously added ¹⁵N¹⁶O^?₂ which occurs during oxidation of ammonia by Nitrosomonas is shown to occur one oxygen at a time. Conditions in which the exchange is diminished (notably the presence of ¹⁴NO^–₂ and CCCP) allowed demonstration that water and dioxygen are each the source of one oxygen in nitrite produced from ¹⁵NH₃. The nitrate produced in the presence of ¹⁸O₂ consisted of 67 and 0% ¹⁵N¹⁸O¹⁶O^? and ¹⁵N¹⁸O¹⁸O^?, respectively. Analysis was made using the ¹⁸O-isotope shift in ¹⁵N-NMR.     

Mechanotransduction activates α5β1 integrin and PI3K/Akt signaling pathways in mandibular osteoblasts

It is unclear how bone cells at different sites detect mechanical loading and how site-specific mechanotransduction affects bone homeostasis. To differentiate the anabolic mechanical responses of mandibular cells from those of calvarial and long bone cells, we isolated osteoblasts from C57B6J mouse bones, cultured them for 1 week, and subjected them to therapeutic low intensity pulsed ultrasound (LIPUS). While the expression of the marker proteins of osteoblasts and osteocytes such as alkaline phosphatase and FGF23, as well as Wnt1 and β-catenin, was equally upregulated, the expression of mandibular osteoblast messages related to bone remodeling and apoptosis differed from that of messages of other osteoblasts, in that the messages encoding the pro-remodeling protein RANKL and the anti-apoptotic protein Bcl-2 were markedly upregulated from the very low baseline levels. Blockage of the PI3K and α₅β₁ integrin pathways showed that the mandibular osteoblast required mechanotransduction downstream of α₅β₁ integrin to upregulate expression of the proteins β-catenin, p-Akt, Bcl-2, and RANKL. Mandibular osteoblasts thus must be mechanically loaded to preserve their capability to promote remodeling and to insure osteoblast survival, both of which maintain intact mandibular bone tissue. In contrast, calvarial Bcl-2 is fully expressed, together with ILK and phosphorylated mTOR, in the absence of LIPUS. The antibody blocking α₅β₁ integrin suppressed both the baseline expression of all calvarial proteins examined and the LIPUS-induced expression of all mandibular proteins examined. These findings indicate that the cellular environment, in addition to the tridermic origin, determines site-specific bone homeostasis through the remodeling and survival of osteoblastic cells. Differentiated cells of the osteoblastic lineage at different sites transmit signals through transmembrane integrins such as α₅β₁ integrin in mandibular osteoblasts, whose signaling may play a major role in controlling bone homeostasis.     

Interactions between environmental stressors: the influence of salinity on host–parasite interactions between Daphnia magna and Pasteuria ramosa

Interactions between environmental stressors play an important role in shaping the health of an organism. This is particularly true in terms of the prevalence and severity of infectious disease, as stressors in combination will not always act to simply decrease the immune function of a host, but may instead interact to compound or even oppose the influence of parasitism on the health of an organism. Here, we explore the impact of environmental stress on host–parasite interactions using the water flea Daphnia magna and it is obligate parasite Pasteuria ramosa. Utilising an ecologically relevant stressor, we focus on the combined effect of salinity and P. ramosa on the fecundity and survival of the host, as well as on patterns of infectivity and the proliferation of the parasite. We show that in the absence of the parasite, host fecundity and survival was highest in the low salinity treatments. Once a parasite was introduced into the environment, however, salinity and parasitism acted antagonistically to influence both host survival and fecundity, and these patterns of disease were unrelated to infection rates or parasite spore loads. By summarising the form of interactions found in the broader Daphnia literature, we highlight how the combined effect of stress and parasitism will vary with the type of stressor, the trait used to describe the health of Daphnia and the host–parasite combination under observation. Our results highlight how the context-dependent nature of interactions between stress and parasitism inevitably complicates the link between environmental factors and the prevalence and severity of disease.     

The roles of PGF2α and PGE2 in regression of the corpus luteum after intrauterine infusion of Arcanobacterium pyogenes in cows

To study the effect of bacteria in the uterus on the fate of the corpus luteum (CL), Arcanobacterium pyogenes was inoculated into the uteri of cows on Day 3 (Day 0 = day of spontaneous ovulation). Plasma concentrations of 13,14-dihydro-15-keto-PGF_2α (PGFM), 13,14-dihydro-15-keto-PGE₂ (PGEM) and progesterone (P₄) were determined. In five cows, the developing CL regressed and first-wave dominant follicles, which normally become atretic, ovulated (Group OV) after bacterial inoculation. In another five cows (Group NOV) and five control cows, the developing CL did not regress and first-wave dominant follicles did not ovulate. In Group OV, PGFM concentrations increased by 126.2 pg/mL (from 36.8 ± 7.8 pg/mL on Day 3 to 163 ± 37.2 pg/mL on Day 6), with an increase ratio of 5.8-fold. Conversely, in Group NOV, PGFM had a greater increase of 198.4 pg/mL (from 128.2 ± 27.8 pg/mL on Day 3 to 326.6 ± 115.1 pg/mL on Day 5), but the increase ratio was only 2.3-fold. Although PGEM tended to increase in both groups, raw increases and increase ratios were small. Bacterial inoculation into the uterus stimulated the release of prostaglandins and affected the fate of the CL; in that regard, the CL was affected more by PGF_2α than by PGE₂, and the increase ratio of PGF_2α was more important than the raw increase.     

1,3-Bis(α-aminoisopropyl)benzene, meta-C6H4(CMe2NH2)2: An N,N-bridging and N,C,N-cyclometalating ligand

Saponification of the bis(carbamic acid ester) 1,3-C₆H₄(CMe₂NHCO₂Me)₂ (1), made by the addition of methanol to commercial 1,3-C₆H₄(CMe₂NCO)₂, yielded the meta-phenylene-based bis(tertiary carbinamine) 1,3-C₆H₄(CMe₂NH₂)₂ (2). Dinuclear [{(η⁴-1,5-C₈H₁₂)RhCl}₂{μ-1,3-C₆H₄(CMe₂NH₂)₂}] (3) resulted from the action of 2 on [{(η⁴-1,5-C₈H₁₂)Rh(μ-Cl)}₂] in toluene. Combination of 2 with PdCl₂ or K₂[PdCl₄] gave the dipalladium macrocycle trans,trans-[{μ-1,3-C₆H₄(CMe₂NH₂)₂}₂(PdCl₂)₂] (4) along with cyclometalated [{2,6-C₆H₃(CMe₂NH₂)₂-κN,κC¹,κN′}PdCl] (5). Substitution of PEt₃ for the labile chlorido ligand of 5 afforded [{2,6-C₆H₃(CMe₂NH₂)₂-κN,κC¹, κN′}Pd(PEt₃)]Cl (6). The crystal structures of the following compounds were determined: bis(carbamic acid ester) 1, ligand 2 as its bis(trifluoroacetate) salt [1,3-C₆H₄(CMe₂NH₃)₂](O₂CCF₃)₂, 2 · (HAc_f)₂, complexes 3 and 6, as well as 1,3-C₆H₄(CMe₂OH)₂ (the diol analogue of 2).     

An insight into major signaling pathways and protein–protein interaction networks involved in the pathogenesis of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is associated with the increase of glucose in the blood rather than being absorbed by the cells. A better understanding of the signaling pathways is necessary to understand the pathophysiology of GDM. This study provides details about a series of signaling pathways and protein–protein interactions involved in the pathogenesis of GDM and their evaluations in GDM development. Protein–protein interactions were found between proteins of several signaling pathways that suggest interlink between these signaling pathways. Protein–protein interactions were generated with high confidence interaction scores based on textmining, cooccurrence, coexpression, neighborhood, gene fusion, experiments, and databases. The dysregulation of signaling pathways may also contribute to the increased risk of complications associated with GDM in the mother and child. Further, studies on signaling pathways involved in the pathogenesis of GDM would help in the development of an effective intervention to prevent GDM along with the identification of key targets for effective therapies in the future.     

Cellular adaptation to nutrient deprivation: crosstalk between the mTORC1 and eIF2α signaling pathways and implications for autophagy

The hostile tumor microenvironment results in the generation of intracellular stresses including hypoxia and nutrient deprivation. In order to adapt to such conditions, the cell utilizes several stress-response mechanisms, including the attenuation of protein synthesis, the inhibition of cellular proliferation, and induction of autophagy. Autophagy leads to the degradation of cellular contents, including damaged organelles and mutant proteins, which the cell can then use as an alternate energy source. Two integral changes to the signaling milieu to promote such a response include inhibition of the mammalian target of rapamycin complex 1 (mTORC1) and phosphorylation of eIF2α. This review will describe how conditions found in the tumor microenvironment regulate mTORC1 as well as eIF2α, the downstream impact of these modifications, and the implications in tumorigenesis. We will then discuss the remarkable similarities and overlapping function of these 2 signaling pathways, focusing on the response to amino acid deprivation, and present a new model involving crosstalk between them based on our recent work.     

Association between two genetic variants of CD226 gene and Cervical Squamous Cell Carcinoma: A case–control study

Cervical carcinoma is a common gynecologic tumor severely influencing the health and life quality of women worldwide. CD226, a costimulatory molecule, is mainly participated in the activation and differentiation of T cells. Recent studies have investigated the association between two genetic variants (rs763361 and rs727088) of CD226 gene and many diseases. In order to evaluate whether these two variants are associated with Cervical Squamous Cell Carcinoma (CSCC), a case–control study including 349 CSCC patients and 380 unrelated healthy controls was carried out to determine the genotypes of these two variants by using the methods of polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) and DNA sequencing methods. Significantly increased CSCC risk was observed to be associated with G allele of rs727088 locus (OR = 1.422, 95% CI = 1.129–1.792). We have also observed that increased CSCC risk was statistically associated with rs727088 polymorphism in a dominant model (OR = 1.41, 95% CI = 1.05–1.89). Results of stratified analysis revealed that both rs763361 and rs727088 polymorphisms were not associated with clinical characters. Collectively, this study supports that rs727088 polymorphism may contribute to increased CSCC susceptibility.     

The effects of prostaglandins E2 and F2α on synaptosomal accumulation and release of 3H-norepinephrine

Prostaglandins (PG) of both the E and F series may serve as modulators of norepinephrine (NE) release from peripheral sympathetic neurons. We have studied the effects of PGE₂ and PGF_2α on the accumulation and release of ³H-NE in the CNS using synaptosomes isolated from rat hypothalami.The release of ³H-NE from synaptosomes superfused with Krebs-Ringer bicarbonate buffer was multiphasic with an initial fast release phase followed by a slower release. Raising KC1 concentration of the superfusion medium to 56mM during the slow release phase is known to stimulate ³H-NE release. PGE₂ (1 × 10^?6M) attenuated ³H-NE release during the fast phase and reduced the amount of ³H-NE released due to KC1 stimulation. At lower concentrations of PGE₂ there was no change in the release profile. PGF_2α was without effect on ³H-NE release at all concentrations tested.The accumulation of ³H-NE was significantly diminished by PGE₂ at a concentration of 1 × 10^?6M, while a lower concentration (1 × 10^?7M) was ineffective. PGF_2α had no effect on ³H-NE accumulation at all concentrations investigated.