Taurine hypomodification underlies mitochondrial tRNATrp-related genetic diseases

Area of Science:

• Biochemistry
• Genetics
• Molecular Biology

Background:

• Human mitochondrial tRNAs (hmtRNAs) require modifications like 5-taurinomethyluridine (τm5U) at position 34 for proper function.
• Mutations in mitochondrial DNA (mtDNA) can lead to genetic diseases, partly due to impaired tRNA modification, such as τm5U hypomodification in tRNALeu(UUR) and tRNALys.
• The impact of other mtDNA variants on τm5U biogenesis in different hmtRNAs remains largely unexplored.

Purpose of the Study:

• To investigate whether pathogenic mtDNA mutations in the MT-TW gene cause defects in the τm5U modification of human mitochondrial tRNATrp.
• To establish a system for monitoring the effects of mtDNA mutations on U34 modification in hmtRNAs.
• To explore potential therapeutic strategies for diseases linked to hmtRNATrp hypomodification.

Main Methods:

• Purification of the Escherichia coli MnmE and MnmG complex (EcMnmEG).
• In vitro analysis of EcMnmEG's ability to incorporate modifications into human mitochondrial tRNATrp (hmtRNATrp).
• Assessment of U34 modification in hmtRNATrp from patients and engineered cell lines with specific mtDNA mutations using base editing.

Main Results:

• Purified EcMnmEG successfully incorporated both 5-carboxymethylaminomethyluridine (cmnm5U) and τm5U into hmtRNATrp.
• In vitro assays showed that several pathogenic mutations in hmtRNATrp led to U34 hypomodification.
• A patient with an m.5541C>T mutation and cell lines with m.5532G>A or m.5545C>T mutations exhibited hmtRNATrp τm5U hypomodification.
• Taurine supplementation ameliorated mitochondrial translation defects in patient-derived cells.

Conclusions:

• This study identifies hmtRNATrp as the third hmtRNA species with mutation-related τm5U hypomodification.
• Pathogenic mtDNA mutations in MT-TW can disrupt hmtRNATrp modification, contributing to disease pathogenesis.
• Taurine supplementation presents a potential therapeutic avenue for hmtRNATrp-related mitochondrial diseases.