The druggable antimalarial target PfDXR : overproduction strategies and kinetic characterization

Plasmodium falciparum 1–deoxy–D–xylulose–5–phosphate reductoisomerase (PfDXR) is a key enzyme in the synthesis of isoprenoids in the malaria parasite, using a pathway that is absent in the human host. This enzyme is receiving attention as it has been validated as a promising drug target. However, an impediment to the characterisation of this enzyme has been the inability to obtain sufficient quantities of the enzyme in a soluble and functional form. The expression of PfDXR from the codon harmonised coding region, under conditions of strongly controlled transcription and induction, resulted in a yield of 2 – 4 mg/L of enzyme, which is 8 to 10–fold higher than previously reported yields. The kinetic parameters Km, Vmax and kcat were determined for PfDXR using an NADPH–dependent assay. Residues K295 and K297, unique to species of Plasmodium and located in the catalytic hatch region; and residues V114 and N115, essential for NADPH binding, were mutated to resemble those found in E. coli DXR. Interestingly, these mutations decreased the substrate affinity of PfDXR to values resembling that of E. coli DXR. PfDXR-K295N, K297S and PfDXR-V114A, N115G demonstrated a decreased ability to turnover substrate by 4–fold and 2-fold respectively in comparison to PfDXR. This study indicates a difference in the role of the catalytic hatch in capturing substrate by species of Plasmodium. The results of this study could contribute to the development of inhibitors of PfDXR.National Research Foundation Grant awarded to AB (Thuthuka Programme) and a SAMI Grant awarded to GLB. LSS was awarded a post–doctoral bursary by the South African Malaria Initiative programme; JG was awarded a PhD bursary by SAMI and National Research Foundation and HJ was awarded an Honours bursary by Rhodes University.http://www.eurekaselect.com/628/journal/protein-amp-peptide-lettershb201

In Silico analysis of malaria parasite databanks for specific genes and motifs associated with immune evasion

In Silica analysis of available biological data is a powerful tool for not only the identification of new genes, but also to study evolutionary relationships and regulatory mechanisms. In this study, a number of bioinformatic tools and techniques were applied on the available sequence data of the malaria parasite, Plasmodium falciparum. In Silica techniques were used for the identification of a genomic sequence tag (GST) matching the facilitated glucose transporter family as assessed by BLAST. The open reading frame encoding the fUll-length glucose transporter gene was subsequently assembled from contig sequences of chromosome 2 of the malaria parasite. The frequency of occurrence of di-, tri- and tetranucleotide sequences in both the coding and non-coding regions of chromosome 2 of P. falciparum was also exhaustively analysed. The relative abundance (observed, compared to expected values) of these oligonucleotide sequences, normalised for the nucleotide base composition, was calculated as an odds ratio and compared to those of other organisms. These relative abundancies are referred to as the organism's genomic signature. The CC•GG and CG-dinucleotides exhibited the highest and the lowest odds ratios, respectively. These genome signatures were shown to be constrained by the codon preference and amino acid abundancies. A number of genes with genomic signatures differing significantly from the average signature were also identified and were deduced to be acquired by lateral transfer from unidentified sources. A definite association between interspaced TGCA tetranucleotides and polymorphic traits of the FC27 allele of merozoite surface antigen 2 (MSA-2) was shown. The observed switching and deletion of a limited number of identical nucleotide sequences of several alleles interspersed between direct repeats, provided clues to potential mechanisms employed by the parasite to affect antigenic polymorphism. The identification of a number of motifs for intragenic (homologous) recombination led us to propose a mechanism by which the parasite achieves antigenic variation in single copy genes. These results have profound implications for the design of candidate anti-malarial vaccines, microsatellite typing and characterisation of proteins mediating these recombination events.Dissertation (MSc (Biochemistry))--University of Pretoria, 2001.Biochemistryunrestricte

Profile of rape victims referred by the court to the Free State Psychiatric Complex, 2003 - 2009

Background. The psychological evaluation of rape victims to determine their competency to testify in court and whether they are capable of consenting to sexual intercourse is challenging, especially when the rape victim is mentally retarded. Objective. To describe the profile of mentally retarded rape victims referred to the Free State Psychiatric Complex (FSPC) in Bloemfontein from 2003 to 2009. Methods. A descriptive retrospective study was conducted. The study consisted of 137 rape victims referred by the court to the FSPC for psychological evaluation from 2003 to 2009. Patient files were used to obtain information. Results. The majority of individuals (n=129; 94.2%) in the cohort were female. The mean age of the participants was 19 years (range 3 - 52). The number of victims evaluated increased from four in 2003 to 36 in 2009. Most participants were diagnosed with moderate (67.2%), followed by severe (18.3%) and mild (14.6%) mental retardation. Only two of the victims were able to give legal consent to sexual intercourse. Only one participant was able to testify in a court of law. A noteworthy finding was that in only 25 (18.2%) cases, a clinical psychologist was subpoenaed to testify in court. Conclusion. The vast majority of mentally retarded rape victims in our cohort, regardless of their level of intellectual functioning, were not able to testify in court and were not able to give informed consent to sexual intercourse