Biology subjects

Amberg-Johnson, K.

Publications and source records attributed to Amberg-Johnson, K..

3 recordsLinked to original sources

bioRxiv2018

A mutagenesis screen for essential plastid biogenesis genes in human malaria parasites

Endosymbiosis has driven major molecular and cellular innovations. Plasmodium spp. parasites that cause malaria contain an essential, non-photosynthetic plastid, the apicoplast, which originated from a secondary (eukaryote-eukaryote) endosymbiosis. To discover organellar pathways with evolutionary and biomedical significance, we performed a mutagenesis screen for essential genes required for apicoplast biogenesis in P. falciparum. Apicoplast-minus mutants were isolated using a chemical rescue that permits conditional disruption of the apicoplast and a new fluorescent reporter for organelle loss. Five candidate genes were validated (out of 12 identified), including a TIM-barrel protein that likely derived from a core metabolic enzyme but evolved a new activity. Our results demonstrate the first forward genetic screen to assign essential cellular functions to unannotated P. falciparum genes. A putative TIM-barrel enzyme and other newly-identified apicoplast biogenesis proteins open opportunities to discover new mechanisms of organelle biogenesis, molecular evolution underlying eukaryotic diversity, and drug targets against multiple parasitic diseases.

cell biology↗

bioRxiv2018

Host cell metabolism contributes to delayed-death kinetics of apicoplast inhibitors in Toxoplasma gondii

Toxoplasma gondii and related human parasites contain an essential plastid organelle called the apicoplast. Clinically-used antibiotics and other inhibitors that disrupt apicoplast biogenesis cause a mysterious \"delayed-death\" phenotype, in which parasite growth is unaffected during the first lytic cycle of inhibitor treatment but is severely inhibited in the second lytic cycle even after drug removal. Critical to understanding the complex downstream cellular effects of these drug classes is the timing of apicoplast loss during inhibitor treatment and how it relates to this peculiar growth phenotype. Here we show that, upon treatment with diverse classes of apicoplast inhibitors, newly-replicated T. gondii parasites in the first lytic cycle initially form apicoplasts with defects in protein import or genome replication and eventually fail to inherit the apicoplast altogether. Despite the accumulation of parasites with defective or missing apicoplasts, growth is unaffected during the first lytic cycle, as previously observed. Strikingly, concomitant inhibition of host cell isoprenoid biosynthesis results in growth inhibition in the first lytic cycle and unmasks the apicoplast defects. These results suggest that defects in and even complete loss of the apicoplast in T. gondii are partially rescued by scavenging of host cell metabolites leading to death that is delayed. Our findings uncover host cell interactions that can alleviate apicoplast inhibition and highlight key differences in \"delayed-death\" inhibitors between T. gondii and Plasmodium falciparum.

microbiology↗

bioRxiv2017

A first-in-class inhibitor of parasite FtsH disrupts plastid biogenesis in human pathogens

The malaria parasite Plasmodium falciparum and related apicomplexan pathogens contain an essential plastid organelle, the apicoplast, which is a key anti-parasitic target. Derived from secondary endosymbiosis, the apicoplast depends on novel, but largely cryptic, mechanisms for protein/lipid import and organelle inheritance during parasite replication. These critical biogenesis pathways present untapped opportunities to discover new parasite-specific drug targets. We used an innovative screen to identify actinonin as having a novel mechanism-of-action inhibiting apicoplast biogenesis. Resistant mutation, chemical-genetic interaction, and biochemical inhibition demonstrate that the unexpected target of actinonin in P. falciparum and Toxoplasma gondii is FtsH1, a homolog of a bacterial membrane AAA+ metalloprotease. Pf FtsH1 is the first novel factor required for apicoplast biogenesis identified in a phenotypic screen. Our findings demonstrate that FtsH1 is a novel and, importantly, druggable antimalarial target. Development of FtsH1 inhibitors will have significant advantages with improved drug kinetics and multistage efficacy against multiple human parasites.

microbiology↗