Mutant/mutation
The mutant expresses a C-terminal 2xcmyc-tagged version of SPATR.

Published in bioRxiv preprint doi: https://doi.org/10.1101/2022.03.06.483110

Protein (function)
The secreted protein with an altered thrombospondin repeat (SPATR) contains two adhesive domains: an atypical thrombospondin type-1 repeat (TSR) and a Type II epidermal growth factor (EGF)-like domain. It is conserved across Plasmodium species and has several orthologues among the Apicomplexa phylum. Although its gene is transcribed in all invasive stages (sporozoites, merozoites and ookinetes), SPATR levels are upregulated in mature sporozoites of both human and rodent infecting Plasmodium species. Moreover, immunolocalization studies detected the protein at the surface of sporozoites of several Plasmodium species, despite the lack of predicted transmembrane domains or a glycosylphosphatidylinositol anchor. Antibodies against the SPATR of P. falciparum also blocked hepatocyte invasion by sporozoites. 

Phenotype
Expression of cmyc-tagged SPATR in sporozoites (as shown by Western analysis)

Mouse polyclonal antibodies against a His-tagged recombinant SPATR detected bands of the approximate predicted size of SPATR (29 or 26 kDa with or without the signal peptide, respectively) in extracts of sporozoites collected from the salivary glands and oocysts, as well as in merozoites. The detection of the protein in WT oocyst-derived sporozoites was unexpected, since previous proteomics studies performed in P. falciparum and P. yoelii had only detected SPATR protein in salivary gland sporozoites, whereas transcripts were present in sporozoites collected from both the oocysts and the salivary  glands, which was suggestive of translational repression. Whether this was due to differences in the parasite species, the technical approaches, or the age of oocyst sporozoites – these were collected from day 19 post-infection onwards in this work, as opposed to days 10–14 in the proteomics studies – remains to be elucidated. Similar band patterns were obtained by Western blot using extracts of sporozoites expressing a c-Myc-tagged SPATR at the C-terminus. Moreover, the tagging of the protein was not detrimental to the parasite as SPATR-myc sporozoites were present in similar numbers compared to controls in oocysts and in the salivary glands and no defects were observed during blood stage growth.

Additional information
 

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