Targeting molecular interactions essential for Plasmodium sexual reproduction

Malaria remains one of the most devastating infectious diseases, killing up to a million people every year. Whereas much progress has been made in understanding the life cycle of the parasite in the human host and in the mosquito vector, significant gaps of knowledge remain. Fertilization of malaria parasites, a process that takes place in the lumen of the mosquito midgut, is poorly understood and the molecular interactions (receptor–ligand) required for Plasmodium fertilization remain elusive. By use of a phage display library, we identified FG1 (Female Gamete peptide 1), a peptide that binds specifically to the surface of female Plasmodium berghei gametes. Importantly, FG1 but not a scrambled version of the peptide, strongly reduces P. berghei oocyst formation by interfering with fertilization. In addition, FG1 also inhibits P. falciparum oocyst formation suggesting that the peptide binds to a molecule on the surface of the female gamete whose structure is conserved. Identification of the molecular interactions disrupted by the FG1 peptide may lead to the development of novel malaria transmission‐blocking strategies.     

Development of a reversed phase high performance liquid chromatography method based on the use of cyclodextrins as mobile phase additives to determine pterostilbene in blueberries

In this work, a reversed phase high performance liquid chromatography (RP-HPLC) method was developed for the determination of pterostilbene in food samples. The novel method is based on the addition of cyclodextrins (CDs) to the mobile phase where the complexation of pterostilbene by CDs is carried out. In order to select the most suitable conditions for the RP-HPLC method, the effect of several physico-chemical parameters on the complexation of pterostilbene by CDs was studied. Our results show that the addition of 12 mM HP-β-CD to a 50:50 (v/v) methanol:water mobile phase at 25°C and pH 7.0 significantly improves the main analytical parameters. In addition, it was seen that pterostilbene forms a 1:1 complex with HP-β-CD, showing an apparent complexation constant of 251±13 M(-1). Finally, in order to study the validity of the proposed method, blueberries were analyzed and the concentration of pterostilbene has been determined.     

Evidence of hybridization in the Argentinean lizards Liolaemus gracilis and Liolaemus bibronii (IGUANIA: LIOLAEMINI): an integrative approach based on genes and morphology

The lizard genus Liolaemus is endemic to temperate South America and includes more than 225 species. Liolaemus gracilis and L. bibronii are closely related species that have large and overlapping geographic distributions, and the objective of this work is to further investigate the L. bibronii–L. gracilis mtDNA paraphyletic pattern previously detected, using an integrative approach, based on mtDNA, nuclear DNA and morphological characters. We identified eight morphological L. bibronii introgressed with L. gracilis mtDNAs, and the reciprocal for one L. gracilis, from six localities in the region of sympatry overlap. The morphological identity of these introgressed individuals was confirmed by diagnostic nuclear markers, and this represents the first well-documented case of interspecific hybridization in the lizard genus Liolaemus. Of the three most likely hypotheses for these observed patterns, we suggest that asymmetrical mtDNA introgression as a result of recent or ongoing hybridization between L. bibronii and L. gracilis is the most likely. This may be due to size selection by L. gracilis female preference for the larger L. bibroni males in sympatry, but this requires experimental confirmation.     

Brucella abortus inhibits IFN-γ-induced FcγRI expression and FcγRI-restricted phagocytosis via toll-like receptor 2 on human monocytes/macrophages

The strategies that allow Brucella abortus to persist for years inside macrophages subverting host immune responses are not completely understood. Immunity against this bacterium relies on the capacity of IFN-γ to activate macrophages, endowing them with the ability to destroy intracellular bacteria. We report here that infection with B. abortus down-modulates the expression of the type I receptor for the Fc portion of IgG (FcγRI, CD64) and FcγRI-restricted phagocytosis regulated by IFN-γ in human monocytes/macrophages. Both phenomena were not dependent on bacterial viability, since they were also induced by heat-killed B. abortus (HKBA), suggesting that they were elicited by a structural bacterial component. Accordingly, a prototypical B. abortus lipoprotein (L-Omp19), but not its unlipidated form, inhibited both CD64 expression and FcγRI-restricted phagocytosis regulated by IFN-γ. Moreover, a synthetic lipohexapeptide that mimics the structure of the protein lipid moiety also inhibited CD64 expression, indicating that any Brucella lipoprotein could down-modulate CD64 expression and FcγRI-restricted phagocytosis. Pre-incubation of monocytes/macrophages with anti-TLR2 mAb blocked the inhibition of the CD64 expression mediated by HKBA and L-Omp19. These results, together with our previous observations establish that B. abortus utilizes its lipoproteins to inhibit the monocytes/macrophages activation mediated by IFN-γ and to subvert host immunonological responses.     

Reactivation of immobilized penicillin G acylase: Influence of cosolvents and catalytic modulators

Reactivation of penicillin G acylase immobilized in glyoxyl-agarose after inactivation was studied with the purpose of increasing the lifespan of the biocatalyst by simple and reproducible strategies, considering unfolding–refolding and direct incubation in reactivation media. Reactivation yields were increased with respect to the control (fully aqueous medium) when cosolvents were added to the reactivation medium at concentrations below 50% (v/v). Best results were obtained with 30% (v/v) ethyleneglycol (EG) in both reactivation strategies. An increase in reactivation yield from 36.0 to 62.8% was obtained using the unfolding–refolding strategy, while an increase from 50.0 to 68.4% was obtained by direct incubation in aqueous media with respect to control. Catalytic modulators were also included in the reactivation medium: competitive inhibitors (phenylacetic acid and 2-thienylacetic acid) caused a reduction while non-competitive (7-ADCA and 6-APA) caused an increase in reactivation yield. Combining cosolvent and catalytic modulators, best results in both strategies were obtained with 30% (v/v) EG plus 100 mM 7-ADCA, where an increase in reactivation yield from 36.0 to 96.0% and from 50.0 to 98.0% was achieved with unfolding–refolding and direct incubation in reactivation media respectively. Apparent reactivation rate was higher in the case of direct incubation in reactivation media, best results being obtained when using 100 mM 7-ADCA and 30% (v/v) EG, with an increase with respect to the control (fully aqueous medium with no modulator) from 0.309 h^?1 to 1.129 h^?1, while for unfolding–refolding strategy increase was only from 0.124 h^?1 to 0.384 h^?1. Results indicate that direct incubation is a better strategy for penicillin G acylase reactivation and opens up the possibility of significantly increasing the operational lifespan of the biocatalyst by operating the reactor with repeated cycles of reaction and reactivation.     

Halofuginone has anti-proliferative effects in acute promyelocytic leukemia by modulating the transforming growth factor beta signaling pathway

Promyelocytic leukemia-retinoic acid receptor alpha (PML-RARα) expression in acute promyelocytic leukemia (APL) impairs transforming growth factor beta (TGFβ) signaling, leading to cell growth advantage. Halofuginone (HF), a low-molecular-weight alkaloid that modulates TGFβ signaling, was used to treat APL cell lines and non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice subjected to transplantation with leukemic cells from human chorionic gonadotrophin-PML-RARα transgenic mice (TG). Cell cycle analysis using incorporated bromodeoxyuridine and 7-amino-actinomycin D showed that, in NB4 and NB4-R2 APL cell lines, HF inhibited cellular proliferation (P<0.001) and induced apoptosis (P = 0.002) after a 24-hour incubation. Addition of TGFβ revealed that NB4 cells were resistant to its growth-suppressive effects and that HF induced these effects in the presence or absence of the cytokine. Cell growth inhibition was associated with up-regulation of TGFβ target genes involved in cell cycle regulation (TGFB, TGFBRI, SMAD3, p15, and p21) and down-regulation of MYC. Additionally, TGFβ protein levels were decreased in leukemic TG animals and HF in vivo could restore TGFβ values to normal. To test the in vivo anti-leukemic activity of HF, we transplanted NOD/SCID mice with TG leukemic cells and treated them with HF for 21 days. HF induced partial hematological remission in the peripheral blood, bone marrow, and spleen. Together, these results suggest that HF has anti-proliferative and anti-leukemic effects by reversing the TGFβ blockade in APL. Since loss of the TGFβ response in leukemic cells may be an important second oncogenic hit, modulation of TGFβ signaling may be of therapeutic interest.     

Characterisation of pks15/1 in clinical isolates of Mycobacterium tuberculosis from Mexico

Tuberculosis (TB) is an infectocontagious respiratory disease caused by members of the Mycobacterium tuberculosis complex. A 7 base pair (bp) deletion in the locus polyketide synthase (pks)15/1 is described as polymorphic among members of the M. tuberculosis complex, enabling the identification of Euro-American, Indo-Oceanic and Asian lineages. The aim of this study was to characterise this locus in TB isolates from Mexico. One hundred twenty clinical isolates were recovered from the states of Veracruz and Estado de Mexico. We determined the nucleotide sequence of a ± 400 bp fragment of the locus pks15/1, while genotypic characterisation was performed by spoligotyping. One hundred and fifty isolates contained the 7 bp deletion, while five had the wild type locus. Lineages X (22%), LAM (18%) and T (17%) were the most frequent; only three (2%) of the isolates were identified as Beijing and two (1%) EAI-Manila. The wild type pks15/1 locus was observed in all Asian lineage isolates tested. Our results confirm the utility of locus pks15/1 as a molecular marker for identifying Asian lineages of the M. tuberculosis complex. This marker could be of great value in the epidemiological surveillance of TB, especially in countries like Mexico, where the prevalence of such lineages is unknown.     

Development of a yeast bioassay to characterize G protein-coupled receptor kinases. Identification of an NH2-terminal region essential for receptor phosphorylation

G protein-coupled receptor kinases (GRKs) specifically bind and phosphorylate the agonist-occupied form of G protein-coupled receptors. To further characterize the mechanism of GRK/receptor interaction, we developed a yeast-based bioassay using strains engineered to functionally express the somatostatin receptor subtype 2 and exhibit agonist-dependent growth. Here, we demonstrate that agonist-promoted growth was effectively inhibited by co-expression with either wild type GRK2 or GRK5, whereas catalytically inactive forms of these kinases were without effect. In an effort to identify residues involved in receptor interaction, we generated a pool of GRK5 mutants and then utilized the bioassay to identify mutants selectively deficient in inhibiting agonist-promoted growth. This resulted in the identification of a large number of mutants, several of which were expressed, purified, and characterized in more detail. Two of the mutants, GRK5-L3Q/K113R and GRK5-T10P, were defective in receptor phosphorylation and also exhibited a partial defect in phospholipid binding and phospholipid-stimulated autophosphorylation of the kinase. In contrast, these mutants had wild type activity in phosphorylating the non-receptor substrate tubulin. To further characterize the function of the NH2-terminal region of GRK5, we generated a deletion mutant lacking residues 2-14 and found that this mutant was also severely impaired in receptor phosphorylation and phospholipid-promoted autophosphorylation. In addition, an NH2-terminal 14-amino acid peptide from GRK5 selectively inhibited receptor phosphorylation by GRK5 but had minimal effect on GRK2 activity. Based on these findings, we propose a model whereby the extreme NH2 terminus of GRK5 mediates phospholipid binding and is required for optimal receptor phosphorylation.