Studies of the FBT family transporters in Leishmania infantum by gene deletion and protein localization.

The protozoan parasite Leishmania has a large family of major facilitator membrane proteins part of the Folate Biopterin Transporter (FBT) family. The chromosome 10 of Leishmania has a cluster of 7 FBT genes including the S-Adenosyl methionine (AdoMet) transporter and the functionally characterized folate transporters FT1 and FT5. Six of the 7 FBT proteins coded by this locus are located at the plasma membrane as determined by gene fusions with the green fluorescent protein. We deleted the whole locus of 7 genes (>30 kb) using CRISPR-Cas9 genome editing as a first step in studying the potential function of the four uncharacterized FBT genes from the locus. This knock out strain was viable, highly resistant to sinefungin (an AdoMet analogue) and to methotrexate (a folate analogue) but not to allopurinol, pentamidine or 5-fluorouracil. We similarly studied another FBT family member whose gene is encoded on chromosome 19. The protein was also located at the plasma membrane and its gene was dispensable for growth and not associated to any of the drug tested. Our work has indicated that large diploid deletion is achievable in Leishmania and the cell lines produced here will serve to better understand the function and putative substrates of these FBT proteins yet to be characterized.