Faculty of Natural and Agricultural Sciences
School of Biological Sciences
Department of Biochemistry
Selected Highlights from Research Findings
Ben Mans obtained several full-length gene sequences coding for tick salivary gland proteins during his PhD study. Bioinformatics-based studies of this information have led to the first-time discovery that anticoagulants and toxins of the sand tampan can be grouped into two distinct and extensively described protein families. This breakthrough discovery has provided a link between tick proteins and a wealth of existing protein structure-activity and three-dimensional structural information. In another study the molecular basis of protein secretion in soft ticks is under study. Since tick salivary gland proteins are involved in disease transmission and tick feeding, these investigations could aid in the rational design of tick control methods.
Contact person: Prof AWH Neitz.
In mammals proteolytic enzymes/proteinases are involved in a large variety of key physiological functions and in ticks there is evidence to show that these enzymes are involved in embryo development and digestion of host red blood cells and proteins. Proteolytic enzymes represent interesting target molecules for tick control, either in the form of a vaccine or an inhibitor. In her MSc studies, Matsatsane Mahlaku has characterised the proteolytic enzymes present in tick salivary glands and found that the main activity was due to the presence of metallo- and serine proteinases. These proteinases were able to hydrolyse fibrinogen as well as disaggregate aggregated platelets and thus probably play an important role in tick feeding. Using a molecular biology approach, Denise Kruger, an Honours student, has obtained the sequence of the cDNA fragment encoding a tick serine proteinase. The deduced partial amino acid sequence was compared to other sequences on the database and the sequence showed high similarity with enzymes involved in invertebrate hemolymph coagulation. The partial sequence is being used to design a gene specific primer and will shortly lead to obtaining the sequence for the whole gene.
Research into the various bioactive substances present in tick salivary glands, could lead to the development of novel therapeutic drugs. The aim of the studies conducted by MSc student, Paul Cheng, is to recombinantly produce and purify the tick fXa- and thrombin inhibitors. This will provide sufficient amounts of the anticoagulants to enable detailed kinetic studies and elucidation of their mechanisms of action. The information obtained from these studies will form the basis for the long-term objective of this research, namely, the production of a chimeric protein exhibiting fXa-, thrombin- and platelet aggregation inhibitory activities.
Contact person: Dr ARM Gaspar.
Several key proteins of the most virulent human malaria parasite, Plasmodium falciparum, are currently being investigated as potential therapeutic targets for the design of new anti-malaria drugs. These studies include the computer-based construction of three-dimensional structural models of the target proteins, experimental validation of critical features of these models and the use of these validated models for virtual screening against libraries of chemical compounds to identify potential parasite-specific inhibitors (drugs). Thus far we have completed, validated and published the modelled structures of three target proteins (triose phosphate isomerase, glucose transporter, ornithine decarboxylase. The modelled structures of three additional target proteins are nearly complete. Tentative inhibitors of triose phosphate isomerase and ornithine decarboxylase have been identified and studies to establish their parasite-specific inhibitory properties are in the early phases of investigation.
Contact person: Prof AI Louw.
The malaria parasite, Plasmodium falciparum, is becoming increasingly resistant to current antimalarial drugs and it is unlikely that a vaccine will be available in the near future. The structural modelling of enzymes involved in the parasite's folate pathway is undertaken by mostly homology-based methods, as well as computer-screening (in silico) of chemical libraries. Promising molecules are screened in recombinantly-expressed enzyme systems, followed by their screening against malaria parasite cultures. Comparitive homology models of enzymes in the folate pathway such as dihydropteroate synthase (DHPS) and dihydrofolate synthase (DHFS) are currently under construction. The project will assist in elucidating the mechanism of drug resistance of DHPS and to identify new targets for anti-malarial drug therapy. It will also lead to an understanding of the structure-function relationships in these enzymes. The ultimate goal of the project is to deliver new lead inhibitory compounds to be used in the pharmaceutical industry.
Contact person: Dr F Joubert.
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