MNMA

MNMA (PF3D7_1019800) is a tRNA-specific 2-thiouridylase that operates in the P. falciparum apicoplast, where it is required for organelle maintenance and parasite survival (PMID:37166116). Direct localization places MNMA in the apicoplast, and its genetic deletion (via chemical bypass) disrupts the organelle and eliminates the apicoplast genome, phenocopying loss of the apicoplast cysteine desulfurase SufS; complementation with a bacterial MnmA together with its cognate cysteine desulfurase indicates that parasite SufS supplies sulfur directly to MNMA for tRNA 2-thio modification (PMID:37166116). MNMA catalyzes the terminal 2-thiouridine (s2U) step of the apicoplast wobble-position xm5s2U tRNA modification pathway, downstream of the xm5-generating enzymes MnmE and MnmG, whose deletion produces the same disrupted-apicoplast phenotype (PMID:39763917). Beyond its role in organelle biology, conditional knockdown of MNMA in an artemisinin-sensitive background hypomodifies s2U and increases artemisinin survival, establishing an epitranscriptomic contribution to the parasite drug response; knockdown also shifts sensitivity to atovaquone, WLL, azithromycin, and fosmidomycin and yields defective schizonts (PMID:38632343).

1. 2023 High

   Establishing where MNMA acts and how it obtains its sulfur substrate resolved whether this thiouridylase functions in the apicoplast and depends on the organellar cysteine desulfurase.

   Evidence Direct apicoplast localization plus chemical-bypass deletion with organelle-maintenance readouts and heterologous complementation using bacterial MnmA and its cognate cysteine desulfurase in P. falciparum

   PMID:37166116

   Open questions at the time

   • Physical/enzymatic interaction between MNMA and SufS not directly reconstituted in vitro
   • The specific apicoplast tRNA substrates modified by MNMA are not enumerated by this study
2. 2024 High

   Determining whether loss of s2U modification alters the drug response tested if MNMA activity is an epitranscriptomic modulator of artemisinin susceptibility rather than purely a housekeeping factor.

   Evidence Conditional knockdown of MNMA in an ART-sensitive P. falciparum Dd2 background with LC-MS/MS tRNA modification analysis, drug survival assays, proteomics/codon-bias analysis, and schizont morphology

   PMID:38632343

   Open questions at the time

   • Mechanism linking s2U hypomodification to altered translation of specific proteins not fully resolved
   • How MNMA hypomodification is triggered in naturally ART-resistant parasites not established
3. 2025 Medium

   Placing MNMA within the xm5s2U biosynthetic pathway clarified that it performs the terminal 2-thio step downstream of the xm5-generating enzymes, unifying the organellar essentiality of the pathway.

   Evidence Chemical-bypass genetic deletion of MNMA, MnmE, and MnmG with apicoplast maintenance assays and comparative genomics in P. falciparum (preprint)

   PMID:39763917

   Open questions at the time

   • Preprint; MNMA-specific results largely corroborate the 2023 eLife study
   • Pathway ordering rests on comparative genomics rather than direct biochemical sequencing of intermediates
   • Direct demonstration that MNMA acts strictly after MnmE/MnmG on the same tRNA not shown

• The precise molecular coupling of SufS-derived sulfur to MNMA catalysis, the full set of apicoplast tRNA substrates, and the translational consequences that link s2U loss to drug-response phenotypes remain to be defined.
• No in vitro reconstitution of MNMA thiouridylase activity
• No structural model of MNMA or of an MNMA–SufS complex
• Codon-level mechanism connecting hypomodification to differential protein expression not established