Solution X-ray scattering highlights discrepancies in Plasmodium multi-aminoacyl-tRNA synthetase complexes

Comparative proteomics uncovers low asparagine content in Plasmodium tRip-KO proteins

tRNAs are not only essential for decoding the genetic code, but their abundance also has a strong impact on the rate of protein production, folding, and on the stability of the translated messenger RNAs. Plasmodium expresses a unique surface protein called tRip, involved in the import of exogenous tRNAs into the parasite. Comparative proteomic analysis of the blood stage of wild-type and tRip-KO variant of P. berghei parasites revealed that downregulated proteins in the mutant parasite are distinguished by a bias in their asparagine content. Furthermore, the demonstration of the possibility of charging host tRNAs with Plasmodium aminoacyl-tRNA synthetases led us to propose that imported host tRNAs participate in parasite protein synthesis. These results also suggest a novel mechanism of translational control in which import of host tRNAs emerge as regulators of gene expression in the Plasmodium developmental cycle and pathogenesis, by enabling the synthesis of asparagine-rich regulatory proteins that efficiently and selectively control the parasite infectivity.

RNA aptamers developed against tRip: A preliminary approach targeting tRNA entry in Plasmodium

Malaria is caused by Plasmodium parasites that multiply inside host cells and can be lethal when P. falciparum is involved. We identified tRip as a membrane protein that facilitates the import of exogenous transfer RNA (tRNA) into the parasite. tRip encompasses a tRNA binding domain exposed on the parasite surface. We used the SELEX approach to isolate high-affinity and specific tRip-binding RNA motifs from a library of random 25 nucleotide-long sequences. In five rounds of combined negative and positive selections, an enriched pool of aptamers was obtained; sequencing revealed that they were all different in their primary sequence; only by comparing their structure predictions did most of the selected aptamers reveal a conserved 5-nucleotide motif sequence. We showed that the integral motif is essential for tRip-binding while the rest of the molecule can be significantly reduced or mutated as long as the motif is presented in a single-stranded region. Such RNA aptamers bind in place of the original tRNA substrate and act as an efficient competitor, suggesting that they can block tRip function and slow parasite development.

Plasmodium, the Apicomplexa Outlier When It Comes to Protein Synthesis

Plasmodium is an obligate intracellular parasite that has numerous interactions with different hosts during its elaborate life cycle. This is also the case for the other parasites belonging to the same phylum Apicomplexa. In this study, we bioinformatically identified the components of the multi-synthetase complexes (MSCs) of several Apicomplexa parasites and modelled their assembly using AlphaFold2. It appears that none of these MSCs resemble the two MSCs that we have identified and characterized in Plasmodium. Indeed, tRip, the central protein involved in the association of the two Plasmodium MSCs is different from its homologues, suggesting also that the tRip-dependent import of exogenous tRNAs is not conserved in other apicomplexan parasites. Based on this observation, we searched for obvious differences that could explain the singularity of Plasmodium protein synthesis by comparing tRNA genes and amino acid usage in the different genomes. We noted a contradiction between the large number of asparagine residues used in Plasmodium proteomes and the single gene encoding the tRNA that inserts them into proteins. This observation remains true for all the Plasmodia strains studied, even those that do not contain long asparagine homorepeats.