PT - JOURNAL ARTICLE AU - Anat Florentin AU - David W Cobb AU - Jillian D Fishburn AU - Paul S Kim AU - Manuel A Fierro AU - Vasant Muralidharan TI - A bacterial chaperone is required for plastid function in malaria parasites AID - 10.1101/080408 DP - 2016 Jan 01 TA - bioRxiv PG - 080408 4099 - http://biorxiv.org/content/early/2016/10/12/080408.short 4100 - http://biorxiv.org/content/early/2016/10/12/080408.full AB - Apicomplexan parasites such as Plasmodium falciparum, the causative agent of malaria, contain a non-photosynthetic plastid known as the apicoplast that functions to produce essential metabolic compounds. It was previously reported that several members of the Clp family of chaperones and proteases localize to the apicoplast. In bacteria and in chloroplasts these proteins form complexes that degrade proteins in a proteasome-like manner to regulate key cellular processes, but their function in the apicoplast is completely unknown. In this study, we generated a conditional mutant of the P. falciparum apicoplast-targeted pfclpc gene and found that under normal conditions it localizes to the apicoplast. Knockdown of PfClpC results in growth inhibition and morphological defects, indicating that PfClpC is essential for parasite viability. Upon inhibition, PfClpC loses its apicoplast localization and appears in vesicle-like structures. Other apicoplast-targeted proteins also localize to these structures, suggesting that organelle integrity is compromised. Addition of isopentynyl pyrophosphate completely rescued the growth inhibition, indicating that the only essential function of PfClpC is related to the apicoplast. Moreover, cellular assays suggest that PfClpC inhibition interferes with the ability of the schizont-stage parasites to properly sort functional apicoplast organelles into daughter-merozoites. These data show that PfClpC is an essential gene that functions to maintain apicoplast integrity.Author Summary The deadly human malaria parasite, Plasmodium falciparum, contains a unique organelle called the apicoplast, a non-photosynthetic plastid that produces vital metabolites. Members of the prokaryotic–derived Clp family were previously reported to localize to the apicoplast. In bacteria and plant chloroplasts, Clp homologs form a proteasome-like complex that degrade proteins but their function in parasite biology is unknown. Here we took a conditional knockdown approach to study an apicoplast localized Clp proteins, PfClpC, which we found to be essential for parasite viability. Inhibition of PfClpC results in a growth arrest phenotype that correlates with a reduced replication rate. We observed that PfClpC localizes to the apicoplast, however upon inhibition it is found dispersed in vesicle-like structures suggesting a complete breakdown of organelle integrity. Our ability to rescue the phenotype by adding an essential apicoplast-derived metabolite proved that the only essential function of PfClpC is linked to apicoplast function. Furthermore, we have found evidence supporting a role for PfClpC in apicoplast sorting into daughter cells. Therefore, we propose PfClpC as a potential drug target due to its essentiality, prokaryotic origin and absence from the human host.