Functional defects of pathogenic human mitochondrial tRNAs related to structural fragility

Aminoacylation of transfer RNAs (tRNAs) is essential for protein synthesis. A growing number of human diseases correlate with point mutations in tRNA genes within the mitochondrial genome. These tRNAs have unique sequences th at suggest they have fragile structures. However, the structural significan ce of pathology-related tRNA mutations and their effects on molecular funct ion have not been explored. Here, opthalmoplegia related mutants of a human mitochondrial tRNA have been investigated. Each mutation replaces either a n A-U or G-C pair in the predicted secondary structure with an A-C pair. Am inoacylation of each mutant tRNA was severely attenuated. Moreover, each st rongly inhibited aminoacylation of the wild type substrate, suggesting that the effects of these mutations might not be bypassed in the potentially he teroplasmic environment of mitochondria. The function of mutant tRNAs was r escued by single compensatory mutations that restored Watson-Crick base pai ring and reintroduced stability into regions of predicted secondary structu re, even though the pairs introduced were different from those found in the wild type tRNA. Thus, functional defects caused by a subset of pathogenic mutations may result from the inherent structural fragility of human mitoch ondrial tRNAs.