Recombinant expression, purification, analysis and immunization of mice with plasmodium yoelii glyceraldehyde-3-phosphate dehydrogenase (rPyGAPDH) and lactate dehydrogenase (rPyLDH) and evaluation of protection against P. berghei challenge.
Khuzwayo, Sinothile Sementha.
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The principal focus in malaria research is the development of an effective malaria vaccine which will help to prevent death and eliminate the disease. This study investigated two plasmodial glycolytic enzymes as possible malaria vaccine candidates. Plasmodium yoelii glyceraldehyde-3-phosphate (rPyGAPDH) and lactate dehydrogenase (rPyLDH) recombinantly as His-tagged fusion proteins were affinity purified using a cobalt affinity matrix. Ethanol has been reported to enhance expression of recombinant proteins in E. coli bacteria. Concentrations of 1%, 2% and 3% (v/v) ethanol were tested for enhancement of rPyLDH and rPyGAPDH expression in both lysogenic broth and terrific broth. Ethanol reduced the overall expression of proteins by inhibiting the growth of PyLDH and PyGAPDH E. coli host cells. The recombinant proteins were evaluated using a metal ion gel shift assay. Both rPyLDH and rPyGAPDH did not show a size shift on the gel following incubation with Cu2+, Co2+ or Ni2+. Both the reduced and non-reduced forms of rPyLDH and rPyGAPDH had similar migration on a 10%, 12.5% and 15% SDS-PAGE gels. Recombinant PyLDH and rPyGAPDH were prepared in Freund’s adjuvants and mice were immunized to evaluate immunogenicity. Both rPyGAPDH and rPyLDH were immunogenic in mice and produced high antibody titers. Mice were immunized with rPyLDH or rPyGAPDH and challenged with P. berghei infection. All PyLDH immunized mice developed high parasitemia and 1/5 of the PyGAPDH immunized mice maintained low parasitemia below 5% throughout the study. Further work includes repeating the immunization and challenge experiments.