Comparative analysis of the pathogenic mechanisms associated with the G8363A and A8296G mutations in the mitochondrial tRNA(Lys) gene.

Abstract

Two mutations (G8363A and A8296G) in the mtDNA (mitochondrial DNA) tRNA(Lys) gene have been associated with severe mitochondrial diseases in a number of reports. Their functional significance, however, remains unknown. We have already shown that homoplasmic cybrids harbouring the A8296G mutation display normal oxidative phosphorylation, although the possibility of a subtle change in mitochondrial respiratory capacity remains an open issue. We have now investigated the pathogenic mechanism of another mutation in the tRNA(Lys) gene (G8363A) by repopulating an mtDNA-less human osteosarcoma cell line with mitochondria harbouring either this genetic variant alone or an unusual combination of the two mutations (A8296G+G8363A). Cybrids homoplasmic for the single G8363A or the A8296G+G8363A mutations have defective respiratory-chain enzyme activities and low oxygen consumption, indicating a severe impairment of the oxidative phosphorylation system. Generation of G8363A cybrids within a wild-type or the A8296G mtDNA genetic backgrounds resulted in an important alteration in the conformation of the tRNA(Lys), not affecting tRNA steady-state levels. Moreover, mutant cybrids have an important decrease in the proportion of amino-acylated tRNA(Lys) and, consequently, mitochondrial protein synthesis is greatly decreased. Our results demonstrate that the pathogenicity of the G8363A mutation is due to a change in the conformation of the tRNA that severely impairs aminoacylation in the absence of changes in tRNA stability. The only effect detected in the A8296G mutation is a moderate decrease in the aminoacylation capacity, which does not affect mitochondrial protein biosynthesis.

• Authors: Belén Bornstein, José Antonio Mas, Clarice Patrono, Miguel Angel Fernández-Moreno, Emiliano González-Vioque, Yolanda Campos, Rosalba Carrozzo, Miguel Angel Martín, Pilar del Hoyo, Filippo M Santorelli, Joaquín Arenas, Rafael Garesse
• Journal: The Biochemical journal (Biochem J) Vol. 387 Issue Pt 3 Pg. 773-8 (May 01 2005) ISSN: 1470-8728 [Electronic] England
• PMID: 15554876 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA, Mitochondrial
• RNA, Transfer, Lys

Topics

• Aminoacylation
• Cell Line, Tumor
• DNA, Mitochondrial (genetics)
• Gene Expression Regulation (genetics)
• Humans
• MERRF Syndrome (genetics, physiopathology)
• Mitochondria (metabolism)
• Mutation
• Phenotype
• Protein Conformation
• RNA, Transfer, Lys (genetics, physiology)