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Profiling γ-irradiated invasive Plasmodium falciparum merozoites using a systems biology approach

ABSTRACT: Plasmodium falciparum malaria severely impacts human health. In order to broaden our understanding of merozoite invasion of erythrocytes which is responsible for clinical disease, a P. falciparum γ-irradiated "long-lived merozoite" (LLM) line was investigated. Cell-sieve purified LLM invaded human erythrocytes with an improved efficiency of 10- to 300-fold greater than wild-type (WT) parasites. A comparison of their genomes identified limited changes in the open reading frame of LLM; while only marginal differences were observed in the transcriptomes. Analysis of their proteomes by quantitative mass-spectrometry identified 446 out of 981 proteins of known or unknown function with a significant change in protein abundance (ANOVA p < 0.05). Furthermore, the relative molar concentration of nearly 1100 merozoite proteins was established. Unfortunately, a specific change being responsible for the LLM phenotype was not identified. However, immunoblot analyses of LLM lysates showed proteolytic processing of some proteins of the MSP1 complex and AMA1 were delayed, suggesting that this delayed proteolysis positively impacted merozoite viability and subsequent invasion.

ORGANISM(S): Anopheles gambiae Plasmodium falciparum

PROVIDER: GSE81818 | GEO | 2018/02/14

REPOSITORIES: GEO

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Project description:Ubiquitylation is a common post translational modification of eukaryotic proteins. Protein ubiquitylation increases in the transition from intracellular schizont to extracellular merozoite in the asexual blood stage cycle of the human malaria parasite, Plasmodium falciparum (Pf). Here, we identify specific ubiquitylation sites of protein substrates in three intracellular parasite stages and extracellular merozoites; a total of 1464 sites in 546 proteins were identified. 469 ubiquitylated proteins were identified in merozoites compared with only 160 in the preceding intracellular schizont stage, indicating a large increase in protein ubiquitylation associated with merozoite maturation. Following merozoite invasion of erythrocytes, few ubiquitylated proteins were detected in the first intracellular ring stage but as parasites matured through trophozoite to schizont stages the extent of ubiquitylation increased. We identified commonly used ubiquitylation motifs and groups of ubiquitylated proteins in specific areas of cellular function, for example merozoite pellicle proteins involved in erythrocyte invasion, exported proteins, and histones. To investigate the importance of ubiquitylation we screened ubiquitin pathway inhibitors in a parasite growth assay and identified the ubiquitin activating enzyme (UBA1 or E1) inhibitor, MLN7243 (TAK-243) to be particularly effective. This small molecule was shown to be a potent inhibitor of recombinant PfUBA1, and a structural homology model of MLN7243 bound to the parasite enzyme highlights avenues for the development of P. falciparum specific inhibitors. We constructed a genetically modified parasite with a rapamycin-inducible functional deletion of uba1; addition of either MLN7243 or rapamycin to the recombinant parasite line resulted in the same phenotype, with parasite development blocked at the schizont stage. These results indicate that the intracellular target of MLN7243 is UBA1, and this activity is essential for the final differentiation of schizonts to merozoites. The ubiquitylation of many merozoite proteins and their disappearance in ring stages are consistent with the idea that ubiquitylation leads to their destruction via the proteasome once their function is complete following invasion, which would allow amino acid recycling in the period prior to the parasite’s elaboration of a new food vacuole.

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Profiling γ-irradiated invasive Plasmodium falciparum merozoites using a systems biology approach

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