The Plasmodium falciparum artemisinin resistance-associated protein Kelch 13 is required for formation of normal cytostomes

Artemisinin (ART) is a quick-killing and effective antimalarial activated by the haem derived from haemoglobin digestion. Mutations in the parasite's Kelch 13 (K13) protein compromise the efficacy of this drug. Recent studies indicate an undefined role for K13 in haemoglobin uptake. Here, we show that K13 is associated with the collar that constricts cytostomal invaginations required for the parasite to ingest host cytosol. Induced mislocalisation of K13 led to the formation of atypical invaginations lacking the cytostomal ring and constricted neck normally associated with cytostomes. Moreover, the levels of haemoglobin degradation products, haem and haemozoin, are decreased when K13 is inactivated. Our findings demonstrate that K13 is required for normal formation and/or stabilisation of the cytostome, and thereby the parasite's uptake of haemoglobin. This is consistent with perturbation of K13 function leading to decreased activation of ART and consequently, reduced killing. ### Competing Interest Statement The authors have declared no competing interest.