title: Mitochondrial phenylalanyl-tRNA synthetase mutations underlie fatal infantile Alpers encephalopathy.
abstract: Next-generation sequencing has turned out to be a powerful tool to uncover genetic basis of childhood mitochondrial disorders. We utilized whole-exome analysis and discovered novel compound heterozygous mutations in FARS2 (mitochondrial phenylalanyl transfer RNA synthetase), encoding the mitochondrial phenylalanyl transfer RNA (tRNA) synthetase (mtPheRS) in two patients with fatal epileptic mitochondrial encephalopathy. The mutations affected highly conserved amino acids, p.I329T and p.D391V. Recently, a homozygous FARS2 variant p.Y144C was reported in a Saudi girl with mitochondrial encephalopathy, but the pathogenic role of the variant remained open. Clinical features, including postnatal onset, catastrophic epilepsy, lactic acidemia, early lethality and neuroimaging findings of the patients with FARS2 variants, resembled each other closely, and neuropathology was consistent with Alpers syndrome. Our structural analysis of mtPheRS predicted that p.I329T weakened ATP binding in the aminoacylation domain, and in vitro studies with recombinant mutant protein showed decreased affinity of this variant to ATP. Furthermore, p.D391V and p.Y144C were predicted to disrupt synthetase function by interrupting the rotation of the tRNA anticodon stem-binding domain from a closed to an open form. In vitro characterization indicated reduced affinity of p.D391V mutant protein to phenylalanine, whereas p.Y144C disrupted tRNA binding. The stability of p.I329T and p.D391V mutants in a refolding assay was impaired. Our results imply that the three FARS2 mutations directly impair aminoacylation function and stability of mtPheRS, leading to a decrease in overall tRNA charging capacity. This study establishes a new genetic cause of infantile mitochondrial Alpers encephalopathy and reports a new mitochondrial aminoacyl-tRNA synthetase as a cause of mitochondrial disease.
authors: Research Programs Unit, Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, 00290 Helsinki, Finland.
authors: Jenni M
authors: JM
authors: Elo
authors: Srujana S
authors: SS
authors: Yadavalli
authors: Liliya
authors: L
authors: Euro
authors: Pirjo
authors: P
authors: Isohanni
authors: Alexandra
authors: A
authors: Götz
authors: Christopher J
authors: CJ
authors: Carroll
authors: Leena
authors: L
authors: Valanne
authors: Fowzan S
authors: FS
authors: Alkuraya
authors: Johanna
authors: J
authors: Uusimaa
authors: Anders
authors: A
authors: Paetau
authors: Eric M
authors: EM
authors: Caruso
authors: Helena
authors: H
authors: Pihko
authors: Michael
authors: M
authors: Ibba
authors: Henna
authors: H
authors: Tyynismaa
authors: Anu
authors: A
authors: Suomalainen
mesh_terms: D000595:Amino Acid Sequence; D000926:Anticodon / Q000378:metabolism; D001483:Base Sequence; D002549:Diffuse Cerebral Sclerosis of Schilder / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D059472:Exome; D005260:Female; D006801:Humans; D007223:Infant; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D028361:Mitochondrial Diseases / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010652:Phenylalanine-tRNA Ligase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017510:Protein Folding; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism
chemical_list: D000926:Anticodon; D024101:Mitochondrial Proteins; D012343:RNA, Transfer; C000611567:FARS2 protein, human; D010652:Phenylalanine-tRNA Ligase