MTO1 (mitochondrial tRNA translation optimization 1) is a catalytic component of the GTPBP3-MTO1 complex that catalyzes 5-taurinomethyluridine (τm5U) modification at the wobble position (U34) of mitochondrial tRNAs 1. This modification is essential for accurate mitochondrial translation and decoding 1. MTO1 works in concert with GTPBP3's GTPase activity to complete τm5U formation on mammalian mt-tRNAs 1. The enzyme requires folate-derived one-carbon units as methyl donors; loss of SHMT2-mediated folate metabolism impairs τm5U biosynthesis, causing ribosome stalling at specific codons and defective oxidative phosphorylation 2. MTO1 deficiency causes combined oxidative phosphorylation deficiency-10 (COXPD10), characterized by lactic acidosis and hypertrophic cardiomyopathy 34. MTO1-deficient mice exhibit complex I deficiency, cardiomyopathy, and bradycardia, mirroring human disease 4. In hematopoietic cells, MTO1 loss impairs mitochondrial oxidative phosphorylation, causing cytosolic iron accumulation, unfolded protein response activation, and disrupted erythroid differentiation 5. MTO1 is ubiquitously expressed but highly elevated in metabolically active tissues 6. Mutations in mt-tRNA genes causing τm5U hypomodification contribute to genetic diseases including deafness-associated mitochondrial mutations and tRNATrp-related disorders, with taurine supplementation showing therapeutic potential 78.