Genetic validation of PfFKBP35 as an antimalarial drug target

Plasmodium falciparum accounts for the majority of over 600’000 malaria-associated deaths annually. Parasites resistant to nearly all antimalarials have emerged and the need for drugs with alternative modes of action is thus undoubted. The FK506-binding protein Pf FKBP35 has gained attention as a promising drug target due to its high affinity to the macrolide compound FK506 (tacrolimus). Whilst there is considerable interest in targeting Pf FKBP35 with small molecules, a genetic validation of this factor as a drug target is missing and its function in parasite biology remains elusive. Here, we show that limiting Pf FKBP35 levels are lethal to P. falciparum and result in a delayed death-like phenotype that is characterized by defective ribosome homeostasis and stalled protein synthesis. Our data furthermore suggest that FK506, unlike the action of this drug in model organisms, exerts its anti-proliferative activity in a Pf FKBP35-independent manner and, using cellular thermal shift assays, we identify putative FK506-targets beyond Pf FKBP35. In addition to revealing first insights into the function of Pf FKBP35, our results show that FKBP-binding drugs can adopt non-canonical modes of action – with major implications for the development of FK506-derived molecules active against Plasmodium parasites and other eukaryotic pathogens. ### Competing Interest Statement The authors have declared no competing interest.