Bargabos, R. | Search bioRxiv

bioRxiv2025

A Chlorinated Diketopiperazine Antibiotic Targets Mycobacterium Tuberculosis DNA Gyrase

We describe a novel macrocyclic peptide, speirobactin, produced by Photorhabdus that selectively kills Mycobacterium tuberculosis. A non-ribosomal peptide synthase (NRPS) containing two linear modules codes for the synthesis of speirobactin. The biosynthetic operon contains a pentapeptide-repeat protein as a resistance gene. Genomic analysis of speirobactin-resistant mutants of M. tuberculosis led to identification of DNA gyrase as the molecular target. The mutations were recreated by allelic replacement and show that DNA gyrase is the only target. Transcriptome analysis of M. tuberculosis treated with antibiotics shows that speirobactin clusters close to fluoroquinolones, supporting its action against the DNA gyrase.

cell biology↗

bioRxiv2021

METTL8 is required for 3-methylcytosine modification in human mitochondrial tRNAs

A subset of eukaryotic tRNAs is methylated in the anticodon loop to form the 3-methylcytosine (m3C) modification. In mammals, the number of tRNAs containing m3C has expanded to include mitochondrial (mt) tRNA-Ser-UGA and mt-tRNA-Thr-UGU. Whereas the enzymes catalyzing m3C formation in nuclear-encoded cytoplasmic tRNAs have been identified, the proteins responsible for m3C modification in mt-tRNAs are unknown. Here, we show that m3C formation in human mt-tRNAs is dependent upon the Methyltransferase-Like 8 (METTL8) enzyme. We find that METTL8 is a mitochondria-associated protein that interacts with mitochondrial seryl-tRNA synthetase along with mt-tRNAs containing m3C. Human cells deficient in METTL8 exhibit loss of m3C modification in mt-tRNAs but not nuclear-encoded tRNAs. Consistent with the mitochondrial import of METTL8, the formation of m3C in METTL8-deficient cells can be rescued by re-expression of wildtype METTL8 but not by a METTL8 variant lacking the N-terminal mitochondrial localization signal. Notably, METTL8-deficiency in human cells causes alterations in the native migration pattern of mt-tRNA-Ser-UGA suggesting a role for m3C in tRNA folding. Altogether, these findings demonstrate that METTL8 is required for m3C formation in mitochondrial tRNAs and uncover a potential role for m3C modification in mitochondrial tRNA structure.

molecular biology↗