Title:
|
The ookinete surface proteome of Plasmodium berghei
|
Ookinete surface proteins are known to be successful targets for transmission blocking vaccines
(TBVs) that can achieve significant reductions in Plasmodium transmission. To date, only three
proteins have been definitively localised to the ookinete surface; P25, P28 and CTRP. To identify
further proteins, this study produced an ookinete surface-enriched proteome (OSEP) of P.
berghei; Cultured and purified ookinetes were surface-biotinylated. Labelled proteins were then
affinity-purified and subjected to high-throughput mass spectrometry (MudPIT). The resulting
proteome shows significant enrichment of known and predicted surface proteins. However, it also
contains known intracellular proteins, due to ookinete permeabilisation during labelling. Twelve
candidate surface proteins were selected from the generated proteome based on their significant
enrichment in the OSEP and the bioinformatic prediction of features associated with surface
proteins. To produce antibodies, DNA immunisation was performed using plasmids encoding
candidate proteins. Antibodies were successfully generated against three proteins, one
recognising an ookinete-specific protein and a second recognising a protein of the asexual stages,
gametocytes and ookinetes. Immunofluorescence failed to localise candidate proteins to either the
ookinete or to other parasite stages. Ookinete-specific expression seen in Western blots, promoted
further work on candidate protein 0250. However, a knockout of this gene failed to result in a
phenotype distinct from that of wild-type parasites and eGFP-tagging failed to localise this
protein. The generated OSEP provides a source of potential ookinete surface proteins. It is hoped
that investigation these proteins will lead to novel targets for TBV and to a deeper understanding
of how the ookinete interacts on a molecular level with its environment
|