Abstract
Maternally inherited diabetes and deafness (MIDD), a subtype of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), is caused by the A3243G point mutation in the human mitochondrial tRNAleu(UUR) (hmt-tRNAleu(UUR)) gene. The purpose of the current research is to compare the secondary and tertiary structures of mutant and wild-type (WT) hmt-tRNAleu(UUR), which is the first step in understanding the molecular mechanism of the pathogenesis caused by this mutation. Thus, the hypothesis of this study is that the tertiary structure of hmt-tRNAleu(UUR) A3243G is different from that of WT hmt-tRNAleu(UUR). This hypothesis was tested by utilizing various freely available web-based modeling and computational tools. The RNAstructure program predicted secondary structures for WT and mutant hmt-tRNAleu(UUR) that differed in the D hairpin, where the A3243G mutation occurs. The RNAComposer program predicted tertiary structures for WT and mutant hmt-tRNAleu(UUR) that differed in the tertiary interactions of nucleotides in the D hairpin with other structural elements of the tRNA. These results support the hypothesis. It is proposed that these structural differences impair the recognition of the tRNA by posttranscriptional modifying enzymes, specifically the taurinomethylation complex. Thus, the wobble position of the anticodon loop (U34) is not taurinomethylated, leading to a deficiency in decoding leucine codons. It is proposed that the resultant leucine-deficient mitochondrial proteins, specifically those in Complex I and IV, are the cause of oxidative phosphorylation deficiency, leading to a decrease in ATP synthesis in -cells, which results in diabetes. Future investigations of hmt-tRNAleu(UUR) structure and associated mechanistic studies will lead to a better understanding of the molecular pathogenesis, which will guide the development of therapeutic strategies for MELAS and MIDD.