Disease associated mutations in mitochondrial precursor tRNAs affect binding, m1R9 methylation and tRNA processing by mtRNase P

ABSTRACT Mitochondrial diseases linked to mutations in mitochondrial(mt) tRNA sequences are abundant. However, the contributions of these tRNA mutations to the development of diseases is mostly unknown. Mutations may affect interactions with (mt)tRNA maturation enzymes or protein synthesis machinery leading to mitochondrial dysfunction. In human mitochondria, the first step of tRNA processing is the removal of the 5’end of precursor tRNAs (pre-tRNA) catalyzed by the three-component enzyme, mtRNase P. Additionally, one sub-component of mtRNase P, mitochondrial RNase P protein 1 (MRPP1) catalyzes methylation of the R9 base in pre-tRNAs. Despite the central role of 5’ end processing in mitochondrial tRNA maturation, the link between mtRNase P and diseases is mostly unexplored. Here we investigate how 11 different human disease-linked mutations in (mt)pre-tRNAs affect the activities of mtRNase P. We find that several mutations weaken the pre-tRNA binding affinity, while the majority of mutations decrease 5’ end processing and methylation activity catalyzed by mtRNase P. Furthermore, all of the investigated mutations in (mt)pre-tRNA Leu(UUR) alter the tRNA fold which contributes to the partial loss of function of mtRNase P. Overall, these results reveal an etiological link between early steps of (mt)tRNA-substrate processing and mitochondrial disease.