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Key J, Gispert S, Koepf G, Steinhoff-Wagner J, Reichlmeir M, Auburger G. Translation Fidelity and Respiration Deficits in CLPP-Deficient Tissues: Mechanistic Insights from Mitochondrial Complexome Profiling. Int J Mol Sci 2023; 24:17503. [PMID: 38139332 PMCID: PMC10743472 DOI: 10.3390/ijms242417503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 12/07/2023] [Accepted: 12/08/2023] [Indexed: 12/24/2023] Open
Abstract
The mitochondrial matrix peptidase CLPP is crucial during cell stress. Its loss causes Perrault syndrome type 3 (PRLTS3) with infertility, neurodegeneration, and a growth deficit. Its target proteins are disaggregated by CLPX, which also regulates heme biosynthesis via unfolding ALAS enzymes, providing access for pyridoxal-5'-phosphate (PLP). Despite efforts in diverse organisms with multiple techniques, CLPXP substrates remain controversial. Here, avoiding recombinant overexpression, we employed complexomics in mitochondria from three mouse tissues to identify endogenous targets. A CLPP absence caused the accumulation and dispersion of CLPX-VWA8 as AAA+ unfoldases, and of PLPBP. Similar changes and CLPX-VWA8 co-migration were evident for mitoribosomal central protuberance clusters, translation factors like GFM1-HARS2, the RNA granule components LRPPRC-SLIRP, and enzymes OAT-ALDH18A1. Mitochondrially translated proteins in testes showed reductions to <30% for MTCO1-3, the mis-assembly of the complex IV supercomplex, and accumulated metal-binding assembly factors COX15-SFXN4. Indeed, heavy metal levels were increased for iron, molybdenum, cobalt, and manganese. RT-qPCR showed compensatory downregulation only for Clpx mRNA; most accumulated proteins appeared transcriptionally upregulated. Immunoblots validated VWA8, MRPL38, MRPL18, GFM1, and OAT accumulation. Co-immunoprecipitation confirmed CLPX binding to MRPL38, GFM1, and OAT, so excess CLPX and PLP may affect their activity. Our data mechanistically elucidate the mitochondrial translation fidelity deficits which underlie progressive hearing impairment in PRLTS3.
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Affiliation(s)
- Jana Key
- Goethe University Frankfurt, University Hospital, Clinic of Neurology, Exp. Neurology, Heinrich Hoffmann Str. 7, 60590 Frankfurt am Main, Germany; (S.G.); (M.R.); (G.A.)
| | - Suzana Gispert
- Goethe University Frankfurt, University Hospital, Clinic of Neurology, Exp. Neurology, Heinrich Hoffmann Str. 7, 60590 Frankfurt am Main, Germany; (S.G.); (M.R.); (G.A.)
| | - Gabriele Koepf
- Goethe University Frankfurt, University Hospital, Clinic of Neurology, Exp. Neurology, Heinrich Hoffmann Str. 7, 60590 Frankfurt am Main, Germany; (S.G.); (M.R.); (G.A.)
| | - Julia Steinhoff-Wagner
- TUM School of Life Sciences, Animal Nutrition and Metabolism, Technical University of Munich, Liesel-Beckmann-Str. 2, 85354 Freising-Weihenstephan, Germany;
| | - Marina Reichlmeir
- Goethe University Frankfurt, University Hospital, Clinic of Neurology, Exp. Neurology, Heinrich Hoffmann Str. 7, 60590 Frankfurt am Main, Germany; (S.G.); (M.R.); (G.A.)
| | - Georg Auburger
- Goethe University Frankfurt, University Hospital, Clinic of Neurology, Exp. Neurology, Heinrich Hoffmann Str. 7, 60590 Frankfurt am Main, Germany; (S.G.); (M.R.); (G.A.)
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Palmer E, Stepien KM, Campbell C, Barton S, Iosifidis C, Ghosh A, Broomfield A, Woodall A, Wilcox G, Sergouniotis PI, Black GC. Clinical, biochemical and molecular analysis in a cohort of individuals with gyrate atrophy. Orphanet J Rare Dis 2023; 18:265. [PMID: 37667371 PMCID: PMC10476330 DOI: 10.1186/s13023-023-02840-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Accepted: 07/21/2023] [Indexed: 09/06/2023] Open
Abstract
BACKGROUND Gyrate atrophy of the choroid and retina is a rare autosomal recessive metabolic disorder caused by biallelic variants in the OAT gene, encoding the enzyme ornithine δ-aminotransferase. Impaired enzymatic activity leads to systemic hyperornithinaemia, which in turn underlies progressive chorioretinal degeneration. In this study, we describe the clinical and molecular findings in a cohort of individuals with gyrate atrophy. METHODS Study participants were recruited through a tertiary UK clinical ophthalmic genetic service. All cases had a biochemical and molecular diagnosis of gyrate atrophy. Retrospective phenotypic and biochemical data were collected using electronic healthcare records. RESULTS 18 affected individuals from 12 families (8 male, 10 female) met the study inclusion criteria. The median age at diagnosis was 8 years (range 10 months - 33 years) and all cases had hyperornithinaemia (median: 800 micromoles/L; range: 458-1244 micromoles/L). Common features at presentation included high myopia (10/18) and nyctalopia (5/18). Ophthalmic findings were present in all study participants who were above the age of 6 years. One third of patients had co-existing macular oedema and two thirds developed pre-senile cataracts. Compliance with dietary modifications was suboptimal in most cases. A subset of participants had extraocular features including a trend towards reduced fat-free mass and developmental delay. CONCLUSIONS Our findings highlight the importance of multidisciplinary care in families with gyrate atrophy. Secondary ophthalmic complications such as macular oedema and cataract formation are common. Management of affected individuals remains challenging due to the highly restrictive nature of the recommended diet and the limited evidence-base for current strategies.
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Affiliation(s)
- Eleanor Palmer
- Manchester Royal Eye Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Karolina M Stepien
- Adult Inherited Metabolic Disorders, Salford Royal NHS Foundation Trust, Salford, Greater Manchester, UK
- Division of Diabetes, Endocrinology and Gastroenterology, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Christopher Campbell
- Manchester Centre for Genomic Medicine, Saint Mary's Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Stephanie Barton
- Manchester Centre for Genomic Medicine, Saint Mary's Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Christos Iosifidis
- Manchester Royal Eye Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Arunabha Ghosh
- Willink Biochemical Genetics, Royal Manchester Children's Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Alexander Broomfield
- Willink Biochemical Genetics, Royal Manchester Children's Hospital, Manchester University NHS Foundation Trust, Manchester, UK
| | - Alison Woodall
- Adult Inherited Metabolic Disorders, Salford Royal NHS Foundation Trust, Salford, Greater Manchester, UK
- Division of Diabetes, Endocrinology and Gastroenterology, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Gisela Wilcox
- Adult Inherited Metabolic Disorders, Salford Royal NHS Foundation Trust, Salford, Greater Manchester, UK
- Division of Diabetes, Endocrinology and Gastroenterology, School of Medical Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Panagiotis I Sergouniotis
- Manchester Royal Eye Hospital, Manchester University NHS Foundation Trust, Manchester, UK.
- Manchester Centre for Genomic Medicine, Saint Mary's Hospital, Manchester University NHS Foundation Trust, Manchester, UK.
- Division of Evolution, Infection and Genomics, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.
| | - Graeme C Black
- Manchester Royal Eye Hospital, Manchester University NHS Foundation Trust, Manchester, UK.
- Manchester Centre for Genomic Medicine, Saint Mary's Hospital, Manchester University NHS Foundation Trust, Manchester, UK.
- Division of Evolution, Infection and Genomics, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK.
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Biochemical and Bioinformatic Studies of Mutations of Residues at the Monomer-Monomer Interface of Human Ornithine Aminotransferase Leading to Gyrate Atrophy of Choroid and Retina. Int J Mol Sci 2023; 24:ijms24043369. [PMID: 36834788 PMCID: PMC9967328 DOI: 10.3390/ijms24043369] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 02/03/2023] [Accepted: 02/06/2023] [Indexed: 02/10/2023] Open
Abstract
Deficit of human ornithine aminotransferase (hOAT), a mitochondrial tetrameric pyridoxal-5'-phosphate (PLP) enzyme, leads to gyrate atrophy of the choroid and retina (GA). Although 70 pathogenic mutations have been identified, only few enzymatic phenotypes are known. Here, we report biochemical and bioinformatic analyses of the G51D, G121D, R154L, Y158S, T181M, and P199Q pathogenic variants involving residues located at the monomer-monomer interface. All mutations cause a shift toward a dimeric structure, and changes in tertiary structure, thermal stability, and PLP microenvironment. The impact on these features is less pronounced for the mutations of Gly51 and Gly121 mapping to the N-terminal segment of the enzyme than those of Arg154, Tyr158, Thr181, and Pro199 belonging to the large domain. These data, together with the predicted ΔΔG values of monomer-monomer binding for the variants, suggest that the proper monomer-monomer interactions seem to be correlated with the thermal stability, the PLP binding site and the tetrameric structure of hOAT. The different impact of these mutations on the catalytic activity was also reported and discussed on the basis of the computational information. Together, these results allow the identification of the molecular defects of these variants, thus extending the knowledge of enzymatic phenotypes of GA patients.
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Balfoort BM, Buijs MJN, Ten Asbroek ALMA, Bergen AAB, Boon CJF, Ferreira EA, Houtkooper RH, Wagenmakers MAEM, Wanders RJA, Waterham HR, Timmer C, van Karnebeek CD, Brands MM. A review of treatment modalities in gyrate atrophy of the choroid and retina (GACR). Mol Genet Metab 2021; 134:96-116. [PMID: 34340878 DOI: 10.1016/j.ymgme.2021.07.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 07/02/2021] [Accepted: 07/23/2021] [Indexed: 12/29/2022]
Abstract
UNLABELLED Gyrate atrophy of the choroid and retina (GACR) is a rare inborn error of amino acid metabolism caused by bi-allelic variations in OAT. GACR is characterised by vision decline in early life eventually leading to complete blindness, and high plasma ornithine levels. There is no curative treatment for GACR, although several therapeutic modalities aim to slow progression of the disease by targeting different steps within the ornithine pathway. No international treatment protocol is available. We systematically collected all international literature on therapeutic interventions in GACR to provide an overview of published treatment effects. METHODS Following the PRISMA guidelines, we conducted a systematic review of the English literature until December 22nd 2020. PubMed and Embase databases were searched for studies related to therapeutic interventions in patients with GACR. RESULTS A total of 33 studies (n = 107 patients) met the inclusion criteria. Most studies were designed as case reports (n = 27) or case series (n = 4). No randomised controlled trials or large cohort studies were found. Treatments applied were protein-restricted diets, pyridoxine supplementation, creatine or creatine precursor supplementation, l-lysine supplementation, and proline supplementation. Protein-restricted diets lowered ornithine levels ranging from 16.0-91.2%. Pyridoxine responsiveness was reported in 30% of included mutations. Lysine supplementation decreased ornithine levels with 21-34%. Quality assessment showed low to moderate quality of the articles. CONCLUSIONS Based primarily on case reports ornithine levels can be reduced by using a protein restricted diet, pyridoxine supplementation (variation-dependent) and/or lysine supplementation. The lack of pre-defined clinical outcome measures and structural follow-up in all included studies impeded conclusions on clinical effectiveness. Future research should be aimed at 1) Unravelling the OAT biochemical pathway to identify other possible pathologic metabolites besides ornithine, 2) Pre-defining GACR specific clinical outcome measures, and 3) Establishing an international historical cohort.
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Affiliation(s)
- Berith M Balfoort
- Department of Paediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Mark J N Buijs
- Department of Clinical Genetics, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Anneloor L M A Ten Asbroek
- Department of Clinical Genetics, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Arthur A B Bergen
- Department of Clinical Genetics, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands; Department of Ophthalmology, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Camiel J F Boon
- Department of Ophthalmology, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands; Department of Ophthalmology, Leiden University Medical Centre, 2333, ZA, Leiden, the Netherlands
| | - Elise A Ferreira
- Department of Paediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Riekelt H Houtkooper
- Laboratory Genetic Metabolic Diseases, Amsterdam Gastroenterology, Endocrinology, and Metabolism, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Margreet A E M Wagenmakers
- Department of Internal Medicine, Centre for Lysosomal and Metabolic Diseases, Erasmus MC, University Medical Centre Rotterdam, the Netherlands
| | - Ronald J A Wanders
- Laboratory Genetic Metabolic Diseases, Amsterdam Gastroenterology, Endocrinology, and Metabolism, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Hans R Waterham
- Laboratory Genetic Metabolic Diseases, Amsterdam Gastroenterology, Endocrinology, and Metabolism, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Corrie Timmer
- Department Endocrinology and Metabolism Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands
| | - Clara D van Karnebeek
- Department of Paediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands; Department of Paediatrics, Radboud Centre for Mitochondrial Medicine, Radboud University Medical Centre, Nijmegen, the Netherlands
| | - Marion M Brands
- Department of Paediatrics, Emma Children's Hospital, Amsterdam UMC, University of Amsterdam, 1105, AZ, Amsterdam, the Netherlands.
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Montioli R, Sgaravizzi G, Desbats MA, Grottelli S, Voltattorni CB, Salviati L, Cellini B. Molecular and Cellular Studies Reveal Folding Defects of Human Ornithine Aminotransferase Variants Associated With Gyrate Atrophy of the Choroid and Retina. Front Mol Biosci 2021; 8:695205. [PMID: 34395527 PMCID: PMC8360850 DOI: 10.3389/fmolb.2021.695205] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Accepted: 07/01/2021] [Indexed: 11/13/2022] Open
Abstract
The deficit of human ornithine aminotransferase (hOAT) is responsible for gyrate atrophy (GA), a rare recessive inherited disorder. Although more than 60 disease-associated mutations have been identified to date, the molecular mechanisms explaining how each mutation leads to the deficit of OAT are mostly unknown. To fill this gap, we considered six representative missense mutations present in homozygous patients concerning residues spread over the hOAT structure. E. coli expression, spectroscopic, kinetic and bioinformatic analyses, reveal that the R154L and G237D mutations induce a catalytic more than a folding defect, the Q90E and R271K mutations mainly impact folding efficiency, while the E318K and C394Y mutations give rise to both folding and catalytic defects. In a human cellular model of disease folding-defective variants, although at a different extent, display reduced protein levels and/or specific activity, due to increased aggregation and/or degradation propensity. The supplementation with Vitamin B6, to mimic a treatment strategy available for GA patients, does not significantly improve the expression/activity of folding-defective variants, in contrast with the clinical responsiveness of patients bearing the E318K mutation. Thus, we speculate that the action of vitamin B6 could be also independent of hOAT. Overall, these data represent a further effort toward a comprehensive analysis of GA pathogenesis at molecular and cellular level, with important relapses for the improvement of genotype/phenotype correlations and the development of novel treatments.
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Affiliation(s)
- Riccardo Montioli
- Section of Biological Chemistry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Giada Sgaravizzi
- Department of Medicine and Surgery, University of Perugia, Perugia, Italy
| | - Maria Andrea Desbats
- Clinical Genetics Unit, Department of Woman and Child Health, University of Padova, Padova, Italy
| | - Silvia Grottelli
- Department of Medicine and Surgery, University of Perugia, Perugia, Italy
| | - Carla Borri Voltattorni
- Section of Biological Chemistry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Leonardo Salviati
- Clinical Genetics Unit, Department of Woman and Child Health, University of Padova, Padova, Italy
| | - Barbara Cellini
- Department of Medicine and Surgery, University of Perugia, Perugia, Italy
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Montioli R, Bellezza I, Desbats MA, Borri Voltattorni C, Salviati L, Cellini B. Deficit of human ornithine aminotransferase in gyrate atrophy: Molecular, cellular, and clinical aspects. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020; 1869:140555. [PMID: 33068755 DOI: 10.1016/j.bbapap.2020.140555] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 10/09/2020] [Accepted: 10/12/2020] [Indexed: 02/06/2023]
Abstract
Gyrate Atrophy (GA) of the choroid and retina (MIM# 258870) is an autosomal recessive disorder due to mutations of the OAT gene encoding ornithine-delta-aminotransferase (OAT), associated with progressive retinal deterioration and blindness. The disease has a theoretical global incidence of approximately 1:1,500,000. OAT is mainly involved in ornithine catabolism in adults, thus explaining the hyperornithinemia as hallmark of the disease. Patients are treated with an arginine-restricted diet, to limit ornithine load, or the administration of Vitamin B6, a precursor of the OAT coenzyme pyridoxal phosphate. Although the clinical and genetic aspects of GA are known for many years, the enzymatic phenotype of pathogenic variants and their response to Vitamin B6, as well as the molecular mechanisms explaining retinal damage, are poorly clarified. Herein, we provide an overview of the current knowledge on the biochemical properties of human OAT and on the molecular, cellular, and clinical aspects of GA.
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Affiliation(s)
- Riccardo Montioli
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy
| | - Ilaria Bellezza
- Department of Experimental Medicine, Section of Physiology and Biochemistry, University of Perugia, Perugia, Italy
| | - Maria Andrea Desbats
- Clinical Genetics Unit, Department of Woman and Child Health, University of Padova, Padova, Italy
| | - Carla Borri Voltattorni
- Department of Neurosciences, Biomedicine and Movement Sciences, Section of Biological Chemistry, University of Verona, Verona, Italy
| | - Leonardo Salviati
- Clinical Genetics Unit, Department of Woman and Child Health, University of Padova, Padova, Italy.
| | - Barbara Cellini
- Department of Experimental Medicine, Section of Physiology and Biochemistry, University of Perugia, Perugia, Italy.
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Jalali H, Najafi M, Khoshaeen A, Mahdavi MR, Mahdavi M. First report of c.425-1G>A mutation in ornithine aminotransferase gene causing gyrate atrophy of the choroid and retina with hyperornithinemia. Eur J Ophthalmol 2020; 31:NP23-NP26. [PMID: 32418451 DOI: 10.1177/1120672120921734] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Gyrate atrophy is a rare autosomal recessive inherited genetic disease. Progressive deterioration of peripheral night vision and blindness are the foremost clinical manifestations of the disease caused by mutations of ornithine aminotransferase gene. CASE The presented case was an 18-year-old male referred for a progressive reduction of visual acuity, which started when the subject was 7 years old, blurred vision, and hypotonic muscles. OBSERVATIONS The findings by liquid chromatography with tandem mass spectrometry and high-performance liquid chromatography methods exhibited a high level of ornithine: 248 μmol/L (reference range: 44-206 μmol/L) and 818 μmol/L (reference: 25-123 μmol/L), respectively. After genetic counseling and conducting further investigation, a novel mutation (c.425-1G>A) in ornithine aminotransferase gene was recognized through whole exome sequencing and the mutation was verified using Sanger sequencing method, which is associated with gyrate atrophy phenotype. CONCLUSION The exact mechanism of chorioretinal atrophy in hyperornithinemia is not known but the increased ornithine level is the clinical manifestation of gyrate atrophy of choroid and retina, muscle weakness, moderate mental retardation, and low cerebral creatine. Pathogenic variant in the ornithine aminotransferase gene associated with gyrate atrophy, may be beneficial as a biomarker to initial diagnosis and treatment of gyrate atrophy disease.
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Affiliation(s)
- Hossein Jalali
- Thalassemia Research Center, Mazandaran University of Medical Sciences, Sari, Iran
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Vanillic Acid Restores Coenzyme Q Biosynthesis and ATP Production in Human Cells Lacking COQ6. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2019; 2019:3904905. [PMID: 31379988 PMCID: PMC6652073 DOI: 10.1155/2019/3904905] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2019] [Revised: 04/30/2019] [Accepted: 05/26/2019] [Indexed: 11/18/2022]
Abstract
Coenzyme Q (CoQ), a redox-active lipid, is comprised of a quinone group and a polyisoprenoid tail. It is an electron carrier in the mitochondrial respiratory chain, a cofactor of other mitochondrial dehydrogenases, and an essential antioxidant. CoQ requires a large set of enzymes for its biosynthesis; mutations in genes encoding these proteins cause primary CoQ deficiency, a clinically and genetically heterogeneous group of diseases. Patients with CoQ deficiency often respond to oral CoQ10 supplementation. Treatment is however problematic because of the low bioavailability of CoQ10 and the poor tissue delivery. In recent years, bypass therapy using analogues of the precursor of the aromatic ring of CoQ has been proposed as a promising alternative. We have previously shown using a yeast model that vanillic acid (VA) can bypass mutations of COQ6, a monooxygenase required for the hydroxylation of the C5 carbon of the ring. In this work, we have generated a human cell line lacking functional COQ6 using CRISPR/Cas9 technology. We show that these cells cannot synthesize CoQ and display severe ATP deficiency. Treatment with VA can recover CoQ biosynthesis and ATP production. Moreover, these cells display increased ROS production, which is only partially corrected by exogenous CoQ, while VA restores ROS to normal levels. Furthermore, we show that these cells accumulate 3-decaprenyl-1,4-benzoquinone, suggesting that in mammals, the decarboxylation and C1 hydroxylation reactions occur before or independently of the C5 hydroxylation. Finally, we show that COQ6 isoform c (transcript NM_182480) does not encode an active enzyme. VA can be produced in the liver by the oxidation of vanillin, a nontoxic compound commonly used as a food additive, and crosses the blood-brain barrier. These characteristics make it a promising compound for the treatment of patients with CoQ deficiency due to COQ6 mutations.
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Montioli R, Paiardini A, Giardina G, Zanzoni S, Cutruzzola F, Cellini B, Borri Voltattorni C. R180T variant of δ-ornithine aminotransferase associated with gyrate atrophy: biochemical, computational, X-ray and NMR studies provide insight into its catalytic features. FEBS J 2019; 286:2787-2798. [PMID: 30957963 DOI: 10.1111/febs.14843] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 02/21/2019] [Accepted: 04/05/2019] [Indexed: 02/01/2023]
Abstract
Among the over 50 gyrate atrophy-causing mutations of ornithine δ-aminotransferase (OAT), the R180T involves an active site residue located at the dimer interface, which in the crystal structure of OAT complexed with 5-fluoromethylornithine engages a salt bridge with the α-carboxylate of the substrate analogue. Starting from the previous finding that no transaminase activity was detected in CHO-K1 cells expressing the R180T variant, here we try to shed light at the protein level on the structural and/or functional defects of the R180T variant. To this aim, the variant has been cloned, expressed, purified and characterized by a combination of biochemical and structural studies. Although the R180T variant shares a similar overall conformation with the wild-type, its crystal structure solved at 1.8 Ǻ reveals slight structural alterations at the active site and at the dimeric interface. These changes are consistent with the spectroscopic and kinetic results, indicating that the variant, as compared with the wild-type OAT, shows (a) an increased Km value for l-ornithine (l-Orn), (b) an altered pyridoxal 5'-phosphate binding mode and affinity and (c) an increased thermostability. In addition, the R180T mutant exhibits a remarkable loss of catalytic activity and is endowed with the ability to catalyse not only the δ-transamination but also, albeit to a lesser extent, the α-transamination of l-Orn. Overall, these data indicate that the slight structural changes caused by the R180T mutation, preventing a proper collocation of l-Orn at the active site of OAT, are responsible for the notable reduction of the catalytic efficiency. ENZYMES: Ornithine aminotransferase EC 2.6.1.13. DATABASES: 6HX7.pdb.
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Affiliation(s)
- Riccardo Montioli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Italy
| | - Alessandro Paiardini
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Giorgio Giardina
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Italy
| | - Francesca Cutruzzola
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Italy
| | - Barbara Cellini
- Department of Experimental Medicine, University of Perugia, Italy
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