The apical polar ring (APR) is a defining cytoskeletal structure in apicomplexan parasites, critical for parasite morphology and host cell invasion. However, its molecular composition and function remain elusive in Plasmodium falciparum. Here we identify and characterize PfAPR3 as an APR-resident protein. Conditional knockout of PfAPR3 reveals its essential role in asexual replication. PfAPR3-knockout parasites contact host red blood cells but fail to form a tight junction, resulting in a complete block in invasion. Using PfAPR3 as bait, we identify three additional APR proteins (PfAPR4, PfCHAKRA and PfAPR5) and delineate APR biogenesis with ultrastructure expansion microscopy. Unlike PfAPR3, PfCHAKRA is critical for cytoskeletal network organization. Iterative ultrastructure expansion microscopy further shows PfCHAKRA at the basal APR until mid-schizogony, with PfAPR3 exhibiting dual apical–basal ring localization during schizogony. These findings define the molecular architecture and function of the APR in P. falciparum and have implications for understanding parasite host cell infection. This study identifies four essential apical polar ring proteins in Plasmodium falciparum that are required for parasite cytoskeletal organization and host cell invasion.
Gurung et al. (Thu,) studied this question.