Discussion

The neglected tropical disease leishmaniasis is caused by infection with the protozoan parasite Leishmania spp. With over 1 million new cases per year, this disease is a significant cause of mortality and morbidity in endemic areas. The Leishmania parasite cycles between a procyclic promastigote stage in the sandfly vector; a host-infective metacyclic promastigote stage which is transferred from vector to mammalian host during a bloodmeal; and an intracellular amastigote stage which resides inside host macrophages.

The BBSome is a protein complex which is associated with molecular trafficking to/from primary cilia and flagella in other eukaryotes. Previous work (Price et al 2013) showed that deletion of one of the subunits, BBS1, from L. major severely reduces parasite virulence in mice. We hypothesise that the Leishmania BBSome is involved in the transportation of macromolecules to the parasite cell surface. We are in the process of testing this hypothesis by analysis of transgenic parasite cell lines with disrupted BBSome function. We have targeted BBS9, a core protein subunit of the BBSome. Our data shows that knocking out the BBS9 gene in L. mexicana causes a significant decrease in cell size, flagellum length and motility in promastigotes. The ability of stationary phase promastigotes to infect THP-1 macrophages is also significantly reduced in BBS9-/- mutant lines compared to the parental line. The next steps in this work are to analyse the effect these changes have on the distribution of macromolecules on the cell surface. We are using biotinylation and streptavidin pull down of cell surface proteins, which will be analysed by mass spectrometry for differences in protein levels.