title: Defective i6A37 modification of mitochondrial and cytosolic tRNAs results from pathogenic mutations in TRIT1 and its substrate tRNA.
abstract: Identifying the genetic basis for mitochondrial diseases is technically challenging given the size of the mitochondrial proteome and the heterogeneity of disease presentations. Using next-generation exome sequencing, we identified in a patient with severe combined mitochondrial respiratory chain defects and corresponding perturbation in mitochondrial protein synthesis, a homozygous p.Arg323Gln mutation in TRIT1. This gene encodes human tRNA isopentenyltransferase, which is responsible for i6A37 modification of the anticodon loops of a small subset of cytosolic and mitochondrial tRNAs. Deficiency of i6A37 was previously shown in yeast to decrease translational efficiency and fidelity in a codon-specific manner. Modelling of the p.Arg323Gln mutation on the co-crystal structure of the homologous yeast isopentenyltransferase bound to a substrate tRNA, indicates that it is one of a series of adjacent basic side chains that interact with the tRNA backbone of the anticodon stem, somewhat removed from the catalytic center. We show that patient cells bearing the p.Arg323Gln TRIT1 mutation are severely deficient in i6A37 in both cytosolic and mitochondrial tRNAs. Complete complementation of the i6A37 deficiency of both cytosolic and mitochondrial tRNAs was achieved by transduction of patient fibroblasts with wild-type TRIT1. Moreover, we show that a previously-reported pathogenic m.7480A>G mt-tRNASer(UCN) mutation in the anticodon loop sequence A36A37A38 recognised by TRIT1 causes a loss of i6A37 modification. These data demonstrate that deficiencies of i6A37 tRNA modification should be considered a potential mechanism of human disease caused by both nuclear gene and mitochondrial DNA mutations while providing insight into the structure and function of TRIT1 in the modification of cytosolic and mitochondrial tRNAs.
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: John W
authors.initials: JW
authors.lastname: Yarham
authors.affiliation: Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Tek N
authors.initials: TN
authors.lastname: Lamichhane
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Angela
authors.initials: A
authors.lastname: Pyle
authors.affiliation: Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Sandy
authors.initials: S
authors.lastname: Mattijssen
authors.affiliation: Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Baruffini
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bruni
authors.affiliation: Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Donnini
authors.affiliation: Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Alex
authors.initials: A
authors.lastname: Vassilev
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Langping
authors.initials: L
authors.lastname: He
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Blakely
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Helen
authors.initials: H
authors.lastname: Griffin
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Mauro
authors.initials: M
authors.lastname: Santibanez-Koref
authors.affiliation: Department of Neurology, Haukeland University Hospital, Bergen, Norway; Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Laurence A
authors.initials: LA
authors.lastname: Bindoff
authors.affiliation: Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: Ileana
authors.initials: I
authors.lastname: Ferrero
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Chinnery
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: McFarland
authors.affiliation: Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Maraia
authors.affiliation: Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics*; D002478:Cells, Cultured; D030401:Cytochrome-c Oxidase Deficiency / Q000235:genetics; D003600:Cytosol; D004272:DNA, Mitochondrial / Q000235:genetics; D004579:Electron Transport / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D008928:Mitochondria / Q000235:genetics; D028361:Mitochondrial Diseases / Q000235:genetics*; D014176:Protein Biosynthesis / Q000235:genetics; D012313:RNA / Q000235:genetics; D000077278:RNA, Mitochondrial; D012343:RNA, Transfer / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D012568:Schizosaccharomyces / Q000201:enzymology / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics; D013466:Sulfurtransferases / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial; D000077278:RNA, Mitochondrial; D029702:Schizosaccharomyces pombe Proteins; D012313:RNA; D012343:RNA, Transfer; D003576:Electron Transport Complex IV; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; C000595656:TRIT1 protein, human; C023197:tRNA isopentenyltransferase; D013466:Sulfurtransferases; C402430:isopentenyl-adenosine i6a thiotransferase