bims-cytox1 2020-02-02 papers

bims-cytox1

Biomed News

on Cytochrome oxidase subunit 1

Issue of 2020–02–02
eight papers selected by
Gavin McStay, Staffordshire University

Multisystem mitochondrial diseases due to mutations in mtDNA-encoded subunits of complex I.
Codon optimization is an essential parameter for the efficient allotopic expression of mtDNA genes.
Alternative splicing of the bicistronic gene molybdenum cofactor synthesis 1 (MOCS1) uncovers a novel mitochondrial protein maturation mechanism.
A meta-analysis and systematic review of Leigh syndrome: clinical manifestations, respiratory chain enzyme complex deficiency, and gene mutations.
Mitochondrial DNA Depletion Syndromes.
Molecular basis of Leigh syndrome: a current look.
Structure of the Bcs1 AAA-ATPase suggests an airlock-like translocation mechanism for folded proteins.
Mitonuclear genomics and aging.

BMC Pediatr. 2020 Jan 29. 20(1): 41

Multisystem mitochondrial diseases due to mutations in mtDNA-encoded subunits of complex I.

Tereza Danhelovska, Hana Kolarova, Jiri Zeman, Hana Hansikova, Manuela Vaneckova, Lukas Lambert, Vendula Kucerova-Vidrova, Kamila Berankova, Tomas Honzik, Marketa Tesarova.

   BACKGROUND: Maternally inherited complex I deficiencies due to mutations in MT-ND genes represent a heterogeneous group of multisystem mitochondrial disorders (MD) with a unfavourable prognosis. The aim of the study was to characterize the impact of the mutations in MT-ND genes, including the novel m.13091 T > C variant, on the course of the disease, and to analyse the activities of respiratory chain complexes, the amount of protein subunits, and the mitochondrial energy-generating system (MEGS) in available muscle biopsies and cultivated fibroblasts.
METHODS: The respiratory chain complex activities were measured by spectrophotometry, MEGS were analysed using radiolabelled substrates, and protein amount by SDS-PAGE or BN-PAGE in muscle or fibroblasts.
RESULTS: In our cohort of 106 unrelated families carrying different mtDNA mutations, we found heteroplasmic mutations in the genes MT-ND1, MT-ND3, and MT-ND5, including the novel variant m.13091 T > C, in 13 patients with MD from 12 families. First symptoms developed between early childhood and adolescence and progressed to multisystem disease with a phenotype of Leigh or MELAS syndromes. MRI revealed bilateral symmetrical involvement of deep grey matter typical of Leigh syndrome in 6 children, cortical/white matter stroke-like lesions suggesting MELAS syndrome in 3 patients, and a combination of cortico-subcortical lesions and grey matter involvement in 4 patients. MEGS indicated mitochondrial disturbances in all available muscle samples, as well as a significantly decreased oxidation of [1-14C] pyruvate in fibroblasts. Spectrophotometric analyses revealed a low activity of complex I and/or complex I + III in all muscle samples except one, but the activities in fibroblasts were mostly normal. No correlation was found between complex I activities and mtDNA mutation load, but higher levels of heteroplasmy were generally found in more severely affected patients.
CONCLUSIONS: Maternally inherited complex I deficiencies were found in 11% of families with mitochondrial diseases in our region. Six patients manifested with Leigh, three with MELAS. The remaining four patients presented with an overlap between these two syndromes. MEGS, especially the oxidation of [1-14C] pyruvate in fibroblasts might serve as a sensitive indicator of functional impairment due to MT-ND mutations. Early onset of the disease and higher level of mtDNA heteroplasmy were associated with a worse prognosis.

Keywords:  Complex I; Leigh syndrome; MEGS; MELAS syndrome; MT-ND genes; Mitochondria; mtDNA

DOI:  https://doi.org/10.1186/s12887-020-1912-x
Redox Biol. 2020 Jan 11. pii: S2213-2317(19)31063-8. [Epub ahead of print]30 101429

Codon optimization is an essential parameter for the efficient allotopic expression of mtDNA genes.

Caitlin J Lewis, Bhavna Dixit, Elizabeth Batiuk, Carter J Hall, Matthew S O'Connor, Amutha Boominathan.

  Mutations in mitochondrial DNA can be inherited or occur de novo leading to several debilitating myopathies with no curative option and few or no effective treatments. Allotopic expression of recoded mitochondrial genes from the nucleus has potential as a gene therapy strategy for such conditions, however progress in this field has been hampered by technical challenges. Here we employed codon optimization as a tool to re-engineer the protein-coding genes of the human mitochondrial genome for robust, efficient expression from the nucleus. All 13 codon-optimized constructs exhibited substantially higher protein expression than minimally-recoded genes when expressed transiently, and steady-state mRNA levels for optimized gene constructs were 5-180 fold enriched over recoded versions in stably-selected wildtype cells. Eight of thirteen mitochondria-encoded oxidative phosphorylation (OxPhos) proteins maintained protein expression following stable selection, with mitochondrial localization of expression products. We also assessed the utility of this strategy in rescuing mitochondrial disease cell models and found the rescue capacity of allotopic expression constructs to be gene specific. Allotopic expression of codon optimized ATP8 in disease models could restore protein levels and respiratory function, however, rescue of the pathogenic phenotype for another gene, ND1 was only partially successful. These results imply that though codon-optimization alone is not sufficient for functional allotopic expression of most mitochondrial genes, it is an essential consideration in their design.

Keywords:  ATP synthase; Allotopic expression; Codon optimization; Gene therapy; Gene transfer; Mitochondrial DNA (mtDNA); Mitochondrial disease; Mitochondrial respiratory chain complex; Protein expression

DOI:  https://doi.org/10.1016/j.redox.2020.101429
J Biol Chem. 2020 Jan 29. pii: jbc.RA119.010720. [Epub ahead of print]

Alternative splicing of the bicistronic gene molybdenum cofactor synthesis 1 (MOCS1) uncovers a novel mitochondrial protein maturation mechanism.

Simon J Mayr, Juliane Röper, Guenter Schwarz.

  Molybdenum cofactor (Moco) biosynthesis is a highly conserved multistep pathway. The first step, the conversion of GTP to cyclic pyranopterin monophosphate (cPMP), requires the bicistronic gene molybdenum cofactor synthesis 1 (MOCS1). Alternative splicing of MOCS1 within exons 1 and 9 produces four different N-terminal and three different C-terminal products (type I-III). Type I splicing results in bicistronic transcripts with two open reading frames, of which only the first, MOCS1A, is translated, whereas type II/III splicing produces MOCS1AB proteins. Here, we first report the cellular localization of alternatively spliced human MOCS1 proteins. Using fluorescence microscopy, fluorescence spectroscopy and cell fractionation experiments, we found that depending on the alternative splicing of exon 1, type I splice variants (MOCS1A) either localize to the mitochondrial matrix (exon 1a) or remain cytosolic (exon 1b). MOCS1A proteins required exon 1a for mitochondrial translocation, but fluorescence microscopy of MOCS1AB variants (types II and III) revealed that they were targeted to mitochondria independently of exon 1 splicing. In the latter case, cell fractionation experiments displayed that mitochondrial matrix import was facilitated via an internal motif overriding the N-terminal targeting signal. Within mitochondria, MOCS1AB underwent proteolytic cleavage resulting in mitochondrial matrix localization of the MOCS1B domain. In conclusion, MOCS1 produces two functional proteins, MOCS1A and MOCS1B, which follow different translocation routes before mitochondrial matrix import for cPMP biosynthesis involving both proteins. MOCS1 protein maturation provides a novel alternative splicing mechanism that ensures the coordinated mitochondrial targeting of two functionally related proteins from a single gene.

Keywords:  S-adenosylmethionine (SAM); alternative splicing; iron-sulfur protein; mitochondrial transport; molybdenum; molybdenum cofactor; radical SAM enzyme

DOI:  https://doi.org/10.1074/jbc.RA119.010720
Medicine (Baltimore). 2020 Jan;99(5): e18634

A meta-analysis and systematic review of Leigh syndrome: clinical manifestations, respiratory chain enzyme complex deficiency, and gene mutations.

Xueli Chang, Yaxin Wu, Jie Zhou, Huaxing Meng, Wei Zhang, Junhong Guo.

Leigh syndrome (also called Leigh disease or subacute necrotizing encephalomyelopathy) is a rare inherited neurometabolic disorder, which affects the central nervous system. This meta-study systematically analyzed clinical manifestations, respiratory chain enzyme complex deficiency, and gene mutations.Literature was searched for publications in MEDLINE, EMBASE, and the China National Knowledge Infrastructure database for meta-analyses of the incidence of clinical symptoms, laboratory assessments, imaging data, muscle biopsy histochemical staining, activity of the mitochondrial respiratory chain enzyme complex, gene mutations, and the association between age at disease onset and type of gene mutations.This study included 5 studies with 385 Leigh syndrome patients. The most common clinical features of Leigh syndrome included elevated blood and/or cerebrospinal fluid (CSF) levels of lactate (72%), developmental retardation (57%), hypotonia (42%), followed by respiratory dysfunction (34%), epileptic seizures (33%), poor feeding (29%), and weakness (27%). Approximately 80% of the patients had deficiencies of the respiratory chain enzyme complex or isolated complex I deficiency (35%), 32% had mitochondrial DNA (mtDNA) mutations, and 38% had nuclear DNA (nDNA) mutations. Patients with nDNA mutations were younger than those with mtDNA mutations (8.82 ± 13.88 vs 26.20 ± 41.11 years, P = .007).The data from the current meta-analysis demonstrated a variety of clinical and molecular manifestations of Leigh syndrome, with upregulated lactate levels in the blood or CSF being the most common feature. Diagnosis of Leigh syndrome could be confirmed using combined enzymatic and genetic analyses.

DOI: https://doi.org/10.1097/MD.0000000000018634
Clin Perinatol. 2020 Mar;pii: S0095-5108(19)30138-1. [Epub ahead of print]47(1): 123-141

Mitochondrial DNA Depletion Syndromes.

Donald Basel.

  Mitochondrial disorders present in a myriad of ways, which causes them to be included in the differential diagnosis for many patients with undiagnosed disease. A subset of mitochondrial disorders are caused by intrinsic defects in the mitochondrial replication machinery, leading to loss of cellular mitochondrial content over time. The diagnosis of mitochondrial disease is complex. Several best-practice guides are available that enable a higher likelihood of detecting a mitochondrial disorder. The application of genomic sequencing and advanced physiologic analysis of the electron transport chain can offer more definitive evidence of mitochondrial dysfunction.

Keywords:  Depletion; External ophthalmoplegia; Mitochondria; Pseudo-obstruction

DOI:  https://doi.org/10.1016/j.clp.2019.10.008
Orphanet J Rare Dis. 2020 Jan 29. 15(1): 31

Molecular basis of Leigh syndrome: a current look.

Manuela Baldo Schubert, Laura Vilarinho.

  Leigh Syndrome (OMIM 256000) is a heterogeneous neurologic disorder due to damage in mitochondrial energy production that usually starts in early childhood. The first description given by Leigh pointed out neurological symptoms in children under 2 years and premature death. Following cases brought some hypothesis to explain the cause due to similarity to other neurological diseases and led to further investigation for metabolic diseases. Biochemical evaluation and specific metabolic profile suggested impairment in energy production (OXPHOS) in mitochondria. As direct approach to involved tissues is not always possible or safe, molecular analysis is a great cost-effective option and, besides biochemical results, is required to confirm the underlying cause of this syndrome face to clinical suspicion. The Next Generation Sequencing (NGS) advance represented a breakthrough in molecular biology allowing simultaneous gene analysis giving short-time results and increasing the variants underlying this syndrome, counting over 75 monogenic causes related so far. NGS provided confirmation of emerging cases and brought up diagnosis in atypical presentations as late-onset cases, which turned Leigh into a heterogeneous syndrome with variable outcomes. This review highlights clinical presentation in both classic and atypical phenotypes, the investigation pathway throughout confirmation emphasizing the underlying genetic heterogeneity and increasing number of genes assigned to this syndrome as well as available treatment.

Keywords:  Leigh syndrome; Leigh-like syndrome; MILS; NARP; OXPHOS; Review

DOI:  https://doi.org/10.1186/s13023-020-1297-9
Nat Struct Mol Biol. 2020 Jan 27.

Structure of the Bcs1 AAA-ATPase suggests an airlock-like translocation mechanism for folded proteins.

Lukas Kater, Nikola Wagener, Otto Berninghausen, Thomas Becker, Walter Neupert, Roland Beckmann.

Some proteins require completion of folding before translocation across a membrane into another cellular compartment. Yet the permeability barrier of the membrane should not be compromised and mechanisms have remained mostly elusive. Here, we present the structure of Saccharomyces cerevisiae Bcs1, an AAA-ATPase of the inner mitochondrial membrane. Bcs1 facilitates the translocation of the Rieske protein, Rip1, which requires folding and incorporation of a 2Fe-2S cluster before translocation and subsequent integration into the bc1 complex. Surprisingly, Bcs1 assembles into exclusively heptameric homo-oligomers, with each protomer consisting of an amphipathic transmembrane helix, a middle domain and an ATPase domain. Together they form two aqueous vestibules, the first being accessible from the mitochondrial matrix and the second positioned in the inner membrane, with both separated by the seal-forming middle domain. On the basis of this unique architecture, we propose an airlock-like translocation mechanism for folded Rip1.

DOI: https://doi.org/10.1038/s41594-019-0364-1
Hum Genet. 2020 Jan 29.

Mitonuclear genomics and aging.

Joseph C Reynolds, Conscience P Bwiza, Changhan Lee.

Our cells operate based on two distinct genomes that are enclosed in the nucleus and mitochondria. The mitochondrial genome presumably originates from endosymbiotic bacteria. With time, a large portion of the original genes in the bacterial genome is considered to have been lost or transferred to the nuclear genome, leaving a reduced 16.5 Kb circular mitochondrial DNA (mtDNA). Traditionally only 37 genes, including 13 proteins, were thought to be encoded within mtDNA, its genetic repertoire is expanding with the identification of mitochondrial-derived peptides (MDPs). The biology of aging has been largely unveiled to be regulated by genes that are encoded in the nuclear genome, whereas the mitochondrial genome remained more cryptic. However, recent studies position mitochondria and mtDNA as an important counterpart to the nuclear genome, whereby the two organelles constantly regulate each other. Thus, the genomic network that regulates lifespan and/or healthspan is likely constituted by two unique, yet co-evolved, genomes. Here, we will discuss aspects of mitochondrial biology, especially mitochondrial communication that may add substantial momentum to aging research by accounting for both mitonuclear genomes to more comprehensively and inclusively map the genetic and molecular networks that govern aging and age-related diseases.

DOI: https://doi.org/10.1007/s00439-020-02119-5