FKBP35 secures ribosome homeostasis in Plasmodium falciparum

Abstract

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 PfFKBP35 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 PfFKBP35 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 PfFKBP35 levels are lethal to P. falciparum and result in a delayed-death phenotype that is characterized by defective ribosome homeostasis and stalled protein translation. We furthermore show that FK506, unlike the role of this drug in model organisms, exerts its anti-proliferative activity in a PfFKBP35-independent manner and, using cellular thermal shift assays, we identify FK506-targets beyond PfFKBP35. In addition to revealing first insights into the function of PfFKBP35, 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.

The Kelch13 compartment contains highly divergent vesicle trafficking proteins in malaria parasites

“…To identify novel K13 compartment proteins we further exploited previously described proximity-dependent biotinylation experiments that had used K13 or the K13 compartment protein Eps15 as bait, selecting enriched proteins not characterized in our previous work [29] (S1 Table ). In order to do this we excluded proteins that (i) had previously been analysed, (ii) were either linked with or had been shown to localise to the inner membrane complex (IMC) or the basal complex (PF3D7_1345600 [60]; PF3D7_0109000 (PhIL1) [61][62][63]; PF3D7_0717600 (IMC32) [64]; PF3D7_0822900 (PIC2) [65], PF3D7_1018200 (PPP8) [65][66][67], (iii) are considered typical DiQ-BioID 'contaminants' (PF3D7_0708400 (HSP90) and PF3D7_1247400 (FKBP35) [29,68]), (iv) localised to the apical polar ring in P. berghei (PF3D7_1141300 (APR1) [69]), (v) localised to the nucleus PF3D7_1247400 (FKBP35) [70,71], (vi) were linked with the apicoplast (PF3D7_0721100 [72]) or (vi) were also present in BioID experiments using Clathrin heavy chain (CHC) as bait [29] (PF3D7_0408100). These selection criteria resulted in a candidate list of thirteen proteins (PF3D7_1438400 (MCA2), PF3D7_1243400, PF3D7_1365800, PF3D7_1447800, PF3D7_1142100, PF3D7_0103100 (VPS51), PF3D7_1329100 (MyoF), PF3D7_1329500, PF3D7_0405700 (UIS14), PF3D7_0907200, PF3D7_0204300, PF3D7_1117900 and PF3D7_1016200), of which ten were chosen for further characterization in this manuscript (Tables 1 and S1).…”