Structural and biochemical consequences of disease causing mutations in human mitochondrial tRNAMet

Abstract

The translational apparatus of human mitochondria requires only 22 tRNAs, which are encoded by the mitochondrial genome. The tRNA genes are hotspots for disease causing mutations. The single tRNAMet (hmtRNAMet) has 3 known disease causing mutations. One of these (U8C) results in the loss of a specific Mg2+ binding site, leading to an incorrectly folded tRNA that is poorly aminoacylated. A second mutation (A37G) in hmtRNAMet is associated with Leber's Hereditary Optical Neuropathy. The A37G mutant, located in the anticodon loop of hmtRNAMet, retains the wild‐type structure, aminoacylation, and binding to EF‐Tu. Because of the proximity of this mutation to the anticodon, it is likely to affect the decoding process. The third mutation (G53A in the T‐stem) results in abnormal mitochondria with defects in energy production. The G53A mutation alters the structure of the tRNA as determined by chemical probing and thermal denaturation. However, these structural alterations are overcome by the human mitochondrial methionyl‐tRNA synthetase and this mutated tRNA can be aminoacylated efficiently. The G53A mutant has a decreased ability to bind EF‐Tu suggesting that it may have a defect in polypeptide chain elongation. The effect of this mutation on the association and dissociation rate constants for its interaction with EF‐Tu and its subsequent delivery to the ribosome is being investigated. (Supported by NIH Grant GM32734)