tRNA modifying enzymes MnmE and MnmG are essential for Plasmodium falciparum apicoplast maintenance

Abstract

The circular genome of the Plasmodium falciparum apicoplast contains a complete minimal set of tRNAs, positioning the apicoplast as an ideal model for studying the fundamental factors required for protein translation. Modifications at tRNA wobble base positions, such as xm5s2U, are critical for accurate protein translation. These modifications are ubiquitously found in tRNAs decoding two-family box codons ending in A or G in prokaryotes and in eukaryotic organelles. Here, we investigated the xm5s2U biosynthetic pathway in the apicoplast organelle of P. falciparum. Through comparative genomics, we identified orthologs of enzymes involved in this process: SufS, MnmA, MnmE, and MnmG. While SufS and MnmA were previously shown to catalyze s2U modifications, we now show that MnmE and MnmG are apicoplast-localized and contain features required for xm5s2U biosynthetic activity. Notably, we found that P. falciparum lacks orthologs of MnmC, MnmL, and MnmM, suggesting that the parasites contain a minimal xm5s2U biosynthetic pathway similar to that found in bacteria with reduced genomes. Deletion of either MnmE or MnmG resulted in apicoplast disruption and parasite death, mimicking the phenotype observed in {Delta}mnmA and {Delta}sufS parasites. Our data strongly support the presence and essentiality of xm5s2U modifications in apicoplast tRNAs. This study advances our understanding of the minimal requirements for protein translation in the apicoplast organelle. ImportanceThe apicoplast of Plasmodium falciparum is an ideal model for studying minimal translation machinery since it contains the fewest number of tRNA isotypes required for protein translation. In such reduced systems, tRNA modifications, particularly at the wobble anticodon position, are critical for proper decoding of mRNA codons by tRNAs. In this study, we investigated the enzymes responsible for the wobble modification xm5s2U in the apicoplast. Our findings reveal that only four enzymes are required in the apicoplast to carry out this modification, similar to the situation found in bacteria with highly reduced genomes. Based on their phylogenetic conservation, these four enzymes have been included in all proposed minimal genome concepts to date and it appears that the apicoplast has retained the same core machinery. Our findings provide novel insight into apicoplast biology and into minimal requirements for protein translation.