Asymmetric Switching in a Homodimeric ABC Transporter: A Simulation Study

ABC transporters are a large family of membrane proteins involved in a variety of cellular processes, including multidrug and tumor resistance and ion channel regulation. Advances in the structural and functional understanding of ABC transporters have revealed that hydrolysis at the two canonical nucleotide-binding sites (NBSs) is co-operative and non-simultaneous. A conserved core architecture of bacterial and eukaryotic ABC exporters has been established, as exemplified by the crystal structure of the homodimeric multidrug exporter Sav1866. Currently, it is unclear how sequential ATP hydrolysis arises in a symmetric homodimeric transporter, since it implies at least transient asymmetry at the NBSs. We show by molecular dynamics simulation that the initially symmetric structure of Sav1866 readily undergoes asymmetric transitions at its NBSs in a pre-hydrolytic nucleotide configuration. MgATP-binding residues and a network of charged residues at the dimer interface are shown to form a sequence of putative molecular switches that allow ATP hydrolysis only at one NBS. We extend our findings to eukaryotic ABC exporters which often consist of two non-identical half-transporters, frequently with degeneracy substitutions at one of their two NBSs. Interestingly, many residues involved in asymmetric conformational switching in Sav1866 are substituted in degenerate eukaryotic NBS. This finding strengthens recent suggestions that the interplay of a consensus and a degenerate NBS in eukaroytic ABC proteins pre-determines the sequence of hydrolysis at the two NBSs

Defining and Detecting Malaria Epidemics in the Highlands of Western Kenya

Epidemic detection algorithms are being increasingly recommended for malaria surveillance in sub-Saharan Africa. We present the results of applying three simple epidemic detection techniques to routinely collected longitudinal pediatric malaria admissions data from three health facilities in the highlands of western Kenya in the late 1980s and 1990s. The algorithms tested were chosen because they could be feasibly implemented at the health facility level in sub-Saharan Africa. Assumptions of these techniques about the normal distribution of admissions data and the confidence intervals used to define normal years were also investigated. All techniques identified two “epidemic” years in one of the sites. The untransformed Cullen method with standard confidence intervals detected the two “epidemic” years in the remaining two sites but also triggered many false alarms. The performance of these methods is discussed and comments made about their appropriateness for the highlands of western Keny

Controlled Human Malaria Infection in Semi-Immune Kenyan Adults (CHMI-SIKA): a study protocol to investigate in vivo Plasmodium falciparum malaria parasite growth in the context of pre-existing immunity [version 2; peer review: 2 approved]

Malaria remains a major public health burden despite approval for implementation of a partially effective pre-erythrocytic malaria vaccine. There is an urgent need to accelerate development of a more effective multi-stage vaccine. Adults in malaria endemic areas may have substantial immunity provided by responses to the blood stages of malaria parasites, but field trials conducted on several blood-stage vaccines have not shown high levels of efficacy. We will use the controlled human malaria infection (CHMI) models with malaria-exposed volunteers to identify correlations between immune responses and parasite growth rates in vivo. Immune responses more strongly associated with control of parasite growth should be prioritized to accelerate malaria vaccine development. We aim to recruit up to 200 healthy adult volunteers from areas of differing malaria transmission in Kenya, and after confirming their health status through clinical examination and routine haematology and biochemistry, we will comprehensively characterize immunity to malaria using >100 blood-stage antigens. We will administer 3,200 aseptic, purified, cryopreserved Plasmodium falciparum sporozoites (PfSPZ Challenge) by direct venous inoculation. Serial quantitative polymerase chain reaction to measure parasite growth rate in vivo will be undertaken. Clinical and laboratory monitoring will be undertaken to ensure volunteer safety. In addition, we will also explore the perceptions and experiences of volunteers and other stakeholders in participating in a malaria volunteer infection study. Serum, plasma, peripheral blood mononuclear cells and whole blood will be stored to allow a comprehensive assessment of adaptive and innate host immunity. We will use CHMI in semi-immune adult volunteers to relate parasite growth outcomes with antibody responses and other markers of host immunity. / Registration: ClinicalTrials.gov identifier NCT02739763

Effects of Earthing up and Pruning Systems on Post-Harvest Quality of Tomato (Solanum lycopersicon)

Tomato is a popular and extensively cultivated vegetable among the economically promising commodities in the horticulture sector in Kenya. It provides a wide variety of nutrients with many health-related benefits.   This study investigated the effect of integration of pruning and earthing up on postharvest. The experiments were carried out in a split-plot arranged in a randomized complete block design (RCBD) and in CRD for both field and laboratory work respectively. Fruit yield data was taken after each harvest. The results from the analysis of variance for the effect of factors (earthing up and pruning system) and their combined effect showed that there was a significant effect on the average weight loss percentage and total soluble solids in both cultivations. The treatments had a significant effect on the average weight loss percentage, total soluble solids, and fruit firmness in both cultivations. The highest fruit weight loss percentages were recorded from all stem pruning system with no earthing up. The highest fruit firmness (3.41 N mm-1 in cultivation 1 and 3.24 N mm-1 in cultivation 2) was recorded from a single stem pruning system and earthing up to 30 cm. The highest total soluble solids (TSS) percentage 6.09 % was recorded in both cultivations under a single stem pruning system and earthing up to 30 cm.  To improve tomato postharvest, farmers are encouraged to consider triple stem pruning system in combination with earthing up to level 30 cm

Reaction of a Polyphosphino Ruthenium(II) Acetate Complex with Grignard Reagents: Halogenation, Alkylation and β-Elimination

(PMe3)4Ru(H)OAc has been prepared from (PPh3)3Ru(H)OAc via phosphine exchange followed by solvent partitioning between acetonitrile and pentane. Complexes of the type (PMe3)4Ru(H)R (R = Et, nPr, nBu, iBu, H) have been synthesized through reaction with the corresponding Grignard reagents, RMgCl, and were found to be moderately stable provided the alkyl group is primary. Treatment with bulkier alkylmagnesium chlorides led instead to the dihydrido complex (PMe3)4RuH2. In some cases, the reaction was complicated by transfer of halide from the Grignard reagent to form, for example, (PMe3)4Ru(H)Cl