Polymorphisms in Plasmodium falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) in Nigerian children 10 years post-adoption of artemisinin-based combination treatments

The emergence and spread of Plasmodium falciparum parasites resistant to artemisinin derivatives and their partners in southeastern Asia threatens malaria control and elimination efforts, and heightens the need for an alternative therapy. We have explored the distribution of P. falciparum chloroquine resistance transporter (Pfcrt) and multidrug-resistant gene 1 (Pfmdr-1) haplotypes 10 years following adoption of artemisinin-based combination therapies in a bid to investigate the possible re-emergence of Chloroquine-sensitive parasites in Nigeria, and investigated the effect of these P. falciparum haplotypes on treatment outcomes of patients treated with artemisinin-based combination therapies. A total of 271 children aged <5 years with uncomplicated falciparum malaria were included in this study. Polymorphisms on codons 72–76 of the Pfcrt gene and codon 86 and 184 of Pfmdr-1 were determined using the high resolution melting assay. Of 240 (88.6%) samples successfully genotyped with HRM for Pfcrt, wildtype C₇₂M₇₄N₇₅K₇₆ (42.9%) and mutant C₇₂I₇₄E₇₅T₇₆ (53.8%) were observed. Also, wildtype N₈₆Y₁₈₄ (62.9%) and mutant N₈₆F₁₈₄ (21.1%), Y₈₆Y₁₈₄ (6.4%), and Y₈₆F₁₈₄ (0.4%) haplotypes of Pfmdr-1 were observed. Measures of responsiveness to ACTs were similar in children infected with P. falciparum crt haplotypes (C₇₂I₇₄E₇₅T₇₆ and C₇₂M₇₄N₇₅K₇₆) and major mdr-1 haplotypes (N₈₆Y₁₈₄, N₈₆F₁₈₄ and Y₈₆Y₁₈₄). Despite a 10 year gap since the malaria treatment policy changed to ACTs, over 50% of the P. falciparum parasites investigated in this study harboured the Chloroquine-resistant C₇₂I₇₄E₇₅T₇₆ haplotype, however this did not compromise the efficacy of artemisinin-based combination therapies. Should complete artemisinin resistance emerge from or spread to Nigeria, chloroquine might not be a good alternative therapy.     

TiO2 Nanocrystals Synthesized by Laser Pyrolysis for the Up‐Scaling of Efficient Solid‐State Dye‐Sensitized Solar Cells

A crucial issue regarding emerging nanotechnologies remains the up‐scaling of new functional nanostructured materials towards their implementation in high performance applications on a large scale. In this context, we demonstrate high efficiency solid‐state dye‐sensitized solar cells prepared from new porous TiO₂ photoanodes based on laser pyrolysis nanocrystals. This strategy exploits a reduced number of processing steps as well as non‐toxic chemical compounds to demonstrate highly porous TiO₂ films. The possibility to easily tune the TiO₂ nanocrystal physical properties allows us to demonstrate all solid‐state dye‐sensitized devices based on a commercial benchmark materials (organic indoline dye and molecular hole transporter) presenting state‐of‐the‐art performance comparable with reference devices based on a commercial TiO₂ paste. In particular, a drastic improvement in pore infiltration, which is found to balance a relatively lower surface area compared to the reference electrode, is evidenced using laser‐synthesized nanocrystals resulting in an improved short‐circuit current density under full sunlight. Transient photovoltage decay measurements suggest that charge recombination kinetics still limit device performance. However, the proposed strategy emphasizes the potentialities of the laser pyrolysis technique for up‐scaling nanoporous TiO₂ electrodes for various applications, especially for solar energy conversion.     

Site-directed mutagenesis in bacteriorhodopsin mutants and their characterization for bioelectrical and biotechnological equipment

Bacteriorhodopsin (BR) mutagenesis plays an important role in the development of BR-based materials and tools with enhanced optical and electrical properties. Previously reported protocols for generating BR mutations are inefficient for the preparation and purification of mutant proteins. Therefore, a series of BR mutations were generated by using improved methods, which are described in further detail. The functional activity of the recombinant proteins was confirmed by spectroscopic and electrochemical assays. Modified proteins with different wavelengths and activities form a foundation for color-sensitive sensors and can be utilized to produce unique bioelectrical and biotechnological tools and materials. The proton-pumping activity of the generated mutant D85E was normal, indicating that the mutant could be used in light batteries. However, mutants D85Q and D85N were almost inactive; and D85N had a prolonged M state, suggesting that it could be utilized in light memories.     

Specific lipids supply critical negative spontaneous curvature--an essential component of native Ca2+-triggered membrane fusion

The Ca²⁺-triggered merger of two apposed membranes is the defining step of regulated exocytosis. CHOL is required at critical levels in secretory vesicle membranes to enable efficient, native membrane fusion: CHOL-sphingomyelin enriched microdomains organize the site and regulate fusion efficiency, and CHOL directly supports the capacity for membrane merger by virtue of its negative spontaneous curvature. Specific, structurally dissimilar lipids substitute for CHOL in supporting the ability of vesicles to fuse: diacylglycerol, αT, and phosphatidylethanolamine support triggered fusion in CHOL-depleted vesicles, and this correlates quantitatively with the amount of curvature each imparts to the membrane. Lipids of lesser negative curvature than cholesterol do not support fusion. The fundamental mechanism of regulated bilayer merger requires not only a defined amount of membrane-negative curvature, but this curvature must be provided by molecules having a specific, critical spontaneous curvature. Such a local lipid composition is energetically favorable, ensuring the necessary “spontaneous” lipid rearrangements that must occur during native membrane fusion—Ca²⁺-triggered fusion pore formation and expansion. Thus, different fusion sites or vesicle types can use specific alternate lipidic components, or combinations thereof, to facilitate and modulate the fusion pore.     

Genome-wide SNP genotyping highlights the role of natural selection in Plasmodium falciparum population divergence

Background

The malaria parasite Plasmodium falciparum exhibits abundant genetic diversity, and this diversity is key to its success as a pathogen. Previous efforts to study genetic diversity in P. falciparum have begun to elucidate the demographic history of the species, as well as patterns of population structure and patterns of linkage disequilibrium within its genome. Such studies will be greatly enhanced by new genomic tools and recent large-scale efforts to map genomic variation. To that end, we have developed a high throughput single nucleotide polymorphism (SNP) genotyping platform for P. falciparum.

Results

Using an Affymetrix 3,000 SNP assay array, we found roughly half the assays (1,638) yielded high quality, 100% accurate genotyping calls for both major and minor SNP alleles. Genotype data from 76 global isolates confirm significant genetic differentiation among continental populations and varying levels of SNP diversity and linkage disequilibrium according to geographic location and local epidemiological factors. We further discovered that nonsynonymous and silent (synonymous or noncoding) SNPs differ with respect to within-population diversity, inter-population differentiation, and the degree to which allele frequencies are correlated between populations.

Conclusions

The distinct population profile of nonsynonymous variants indicates that natural selection has a significant influence on genomic diversity in P. falciparum, and that many of these changes may reflect functional variants deserving of follow-up study. Our analysis demonstrates the potential for new high-throughput genotyping technologies to enhance studies of population structure, natural selection, and ultimately enable genome-wide association studies in P. falciparum to find genes underlying key phenotypic traits.     

The case for selection at CCR5-Delta32

The C-C chemokine receptor 5, 32 base-pair deletion (CCR5-Delta32) allele confers strong resistance to infection by the AIDS virus HIV. Previous studies have suggested that CCR5-Delta32 arose within the past 1,000 y and rose to its present high frequency (5%-14%) in Europe as a result of strong positive selection, perhaps by such selective agents as the bubonic plague or smallpox during the Middle Ages. This hypothesis was based on several lines of evidence, including the absence of the allele outside of Europe and long-range linkage disequilibrium at the locus. We reevaluated this evidence with the benefit of much denser genetic maps and extensive control data. We find that the pattern of genetic variation at CCR5-Delta32 does not stand out as exceptional relative to other loci across the genome. Moreover using newer genetic maps, we estimated that the CCR5-Delta32 allele is likely to have arisen more than 5,000 y ago. While such results can not rule out the possibility that some selection may have occurred at C-C chemokine receptor 5 (CCR5), they imply that the pattern of genetic variation seen at CCR5-Delta32 is consistent with neutral evolution. More broadly, the results have general implications for the design of future studies to detect the signs of positive selection in the human genome.     

GB Virus C Coinfections in West African Ebola Patients

In 49 patients with known Ebola virus disease outcomes during the ongoing outbreak in Sierra Leone, 13 were coinfected with the immunomodulatory pegivirus GB virus C (GBV-C). Fifty-three percent of these GBV-C⁺ patients survived; in contrast, only 22% of GBV-C⁻ patients survived. Both survival and GBV-C status were associated with age, with older patients having lower survival rates and intermediate-age patients (21 to 45 years) having the highest rate of GBV-C infection. Understanding the separate and combined effects of GBV-C and age on Ebola virus survival may lead to new treatment and prevention strategies, perhaps through age-related pathways of immune activation.