scholarly journals Structure of the human frataxin-bound iron-sulfur cluster assembly complex provides insight into its activation mechanism

2019 ◽  
Author(s):  
Nicholas G. Fox ◽  
Xiaodi Yu ◽  
Xidong Feng ◽  
Henry J. Bailey ◽  
Alain Martelli ◽  
...  
Keyword(s):  
De Novo ◽  
Neurodegenerative Disorder ◽  
Acyl Carrier Protein ◽  
Local Environment ◽  
Zinc Ion ◽  
Activation Mechanism ◽  
Cluster Assembly ◽  
Loss Of Function ◽  
Iron Sulfur ◽  
Zinc Inhibition

AbstractIron-sulfur clusters (ISC) are essential in all life forms and carry out many crucial cellular functions. The core machinery for de novo ISC biosynthesis, located in the mitochondria matrix, is a five-protein complex containing the cysteine desulfurase NFS1 that is activated by frataxin (FXN), scaffold protein ISCU, accessory protein ISD11, and acyl-carrier protein ACP. Deficiency in FXN leads to the loss-of-function neurodegenerative disorder Friedreich’s ataxia (FRDA). Recently crystal structures depicting the inactive 3- and 4-way sub-complexes of the ISC biosynthesis machinery, lacking the key activator FXN, have been determined. Here, the 3.2 Å resolution cryo-electron microscopy structure of the FXN-bound active human complex, containing two copies of the NFS1-ISD11-ACP-ISCU-FXN hetero-pentamer, delineates for the first time in any organism the interactions of FXN with the component proteins. FXN binds at the interface of two NFS1 and one ISCU subunits, modifying the local environment of a bound zinc ion that would otherwise inhibit NFS1 activity in complexes without FXN. Our structure sheds light on how FXN facilitates ISC production through unlocking the zinc inhibition and stabilizing key loop conformations of NFS1 and ISCU at the protein-protein interfaces, and offers an explanation of how FRDA clinical mutations affect complex formation and FXN activation.

scholarly journals De novo pathogenic variant in SETX causes a rapidly progressive neurodegenerative disorder of early childhood-onset with severe axonal polyneuropathy

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Aristides Hadjinicolaou ◽  
Kathie J. Ngo ◽  
Daniel Y. Conway ◽  
John P. Provias ◽  
Steven K. Baker ◽  
...  
Keyword(s):  
Network Analysis ◽  
De Novo ◽  
Neurodegenerative Disorder ◽  
Neurological Diseases ◽  
Patient Data ◽  
Loss Of Function ◽  
Sequencing Data ◽  
Gene Variation ◽  
Transcriptional Signature ◽  
Pathogenic Variants

AbstractPathogenic variants in SETX cause two distinct neurological diseases, a loss-of-function recessive disorder, ataxia with oculomotor apraxia type 2 (AOA2), and a dominant gain-of-function motor neuron disorder, amyotrophic lateral sclerosis type 4 (ALS4). We identified two unrelated patients with the same de novo c.23C > T (p.Thr8Met) variant in SETX presenting with an early-onset, severe polyneuropathy. As rare private gene variation is often difficult to link to genetic neurological disease by DNA sequence alone, we used transcriptional network analysis to functionally validate these patients with severe de novo SETX-related neurodegenerative disorder. Weighted gene co-expression network analysis (WGCNA) was used to identify disease-associated modules from two different ALS4 mouse models and compared to confirmed ALS4 patient data to derive an ALS4-specific transcriptional signature. WGCNA of whole blood RNA-sequencing data from a patient with the p.Thr8Met SETX variant was compared to ALS4 and control patients to determine if this signature could be used to identify affected patients. WGCNA identified overlapping disease-associated modules in ALS4 mouse model data and ALS4 patient data. Mouse ALS4 disease-associated modules were not associated with AOA2 disease modules, confirming distinct disease-specific signatures. The expression profile of a patient carrying the c.23C > T (p.Thr8Met) variant was significantly associated with the human and mouse ALS4 signature, confirming the relationship between this SETX variant and disease. The similar clinical presentations of the two unrelated patients with the same de novo p.Thr8Met variant and the functional data provide strong evidence that the p.Thr8Met variant is pathogenic. The distinct phenotype expands the clinical spectrum of SETX-related disorders.

Mechanisms of Mitochondrial Iron-Sulfur Protein Biogenesis

2020 ◽  
Vol 89 (1) ◽  
pp. 471-499 ◽  
Author(s):  
Roland Lill ◽  
Sven-A. Freibert
Keyword(s):  
Molecular Mechanisms ◽  
De Novo ◽  
Lipid Synthesis ◽  
Cluster Assembly ◽  
Iron Sulfur Cluster ◽  
Atp Production ◽  
Cellular Iron ◽  
Iron Sulfur ◽  
Sulfur Protein ◽  
S Proteins

Mitochondria are essential in most eukaryotes and are involved in numerous biological functions including ATP production, cofactor biosyntheses, apoptosis, lipid synthesis, and steroid metabolism. Work over the past two decades has uncovered the biogenesis of cellular iron-sulfur (Fe/S) proteins as the essential and minimal function of mitochondria. This process is catalyzed by the bacteria-derived iron-sulfur cluster assembly (ISC) machinery and has been dissected into three major steps: de novo synthesis of a [2Fe-2S] cluster on a scaffold protein; Hsp70 chaperone–mediated trafficking of the cluster and insertion into [2Fe-2S] target apoproteins; and catalytic conversion of the [2Fe-2S] into a [4Fe-4S] cluster and subsequent insertion into recipient apoproteins. ISC components of the first two steps are also required for biogenesis of numerous essential cytosolic and nuclear Fe/S proteins, explaining the essentiality of mitochondria. This review summarizes the molecular mechanisms underlying the ISC protein–mediated maturation of mitochondrial Fe/S proteins and the importance for human disease.

scholarly journals Identification of IscU residues critical for de novo iron–sulfur cluster assembly

2019 ◽  
Vol 112 (6) ◽  
pp. 1769-1783
Author(s):  
Naoyuki Tanaka ◽  
Eiki Yuda ◽  
Takashi Fujishiro ◽  
Kei Hirabayashi ◽  
Kei Wada ◽  
...  
Keyword(s):  
De Novo ◽  
Cluster Assembly ◽  
Iron Sulfur Cluster ◽  
Sulfur Cluster ◽  
Iron Sulfur

scholarly journals Structure of the human frataxin-bound iron-sulfur cluster assembly complex provides insight into its activation mechanism

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Nicholas G. Fox ◽  
Xiaodi Yu ◽  
Xidong Feng ◽  
Henry J. Bailey ◽  
Alain Martelli ◽  
...  
Keyword(s):  
Activation Mechanism ◽  
Cluster Assembly ◽  
Iron Sulfur Cluster ◽  
Sulfur Cluster ◽  
Iron Sulfur ◽  
Insight Into

scholarly journals N-terminal tyrosine of ISCU2 triggers [2Fe-2S] cluster synthesis by ISCU2 dimerization

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sven-A. Freibert ◽  
Michal T. Boniecki ◽  
Claudia Stümpfig ◽  
Vinzent Schulz ◽  
Nils Krapoth ◽  
...  
Keyword(s):  
De Novo ◽  
Cluster Formation ◽  
Cluster Assembly ◽  
Cysteine Desulfurase ◽  
Iron Sulfur Cluster ◽  
Mutant Proteins ◽  
Iron Sulfur ◽  
Initial Iron ◽  
Oppositely Charged

AbstractSynthesis of iron-sulfur (Fe/S) clusters in living cells requires scaffold proteins for both facile synthesis and subsequent transfer of clusters to target apoproteins. The human mitochondrial ISCU2 scaffold protein is part of the core ISC (iron-sulfur cluster assembly) complex that synthesizes a bridging [2Fe-2S] cluster on dimeric ISCU2. Initial iron and sulfur loading onto monomeric ISCU2 have been elucidated biochemically, yet subsequent [2Fe-2S] cluster formation and dimerization of ISCU2 is mechanistically ill-defined. Our structural, biochemical and cell biological experiments now identify a crucial function of the universally conserved N-terminal Tyr35 of ISCU2 for these late reactions. Mixing two, per se non-functional ISCU2 mutant proteins with oppositely charged Asp35 and Lys35 residues, both bound to different cysteine desulfurase complexes NFS1-ISD11-ACP, restores wild-type ISCU2 maturation demonstrating that ionic forces can replace native Tyr-Tyr interactions during dimerization-induced [2Fe-2S] cluster formation. Our studies define the essential mechanistic role of Tyr35 in the reaction cycle of de novo mitochondrial [2Fe-2S] cluster synthesis.

scholarly journals Zinc(II) binding on human wild-type ISCU and Met140 variants modulates Fe-S complex activity

2018 ◽  
Author(s):  
Nicholas G. Fox ◽  
Alain Martelli ◽  
Joseph F. Nabhan ◽  
Jay Janz ◽  
Oktawia Borkowska ◽  
...  
Keyword(s):  
Protein Complex ◽  
De Novo ◽  
Cluster Assembly ◽  
Wild Type ◽  
Complex Activity ◽  
Cysteine Desulfurase ◽  
Iron Sulfur ◽  
Ethylenediaminetetracetic Acid ◽  
Piperazineethanesulfonic Acid

ABSTRACTThe human de novo iron-sulfur (Fe-S) assembly complex consists of the cysteine desulfurase NFS1, accessory protein ISD11, scaffold protein ISCU, and allosteric activator frataxin (FXN). FXN has been shown to bind the NFS1-ISD11-ISCU complex (SDU), to activate the desulfurase activity and thus Fe-S cluster biosynthesis. Conversely, in the absence of FXN, the NFS1-ISD11 (SD) complex was reported to be inhibited by the binding of recombinant ISCU. Here, we show that recombinant ISCU binds zinc(II) ion, and that the presence of zinc in as-isolated ISCU has impacts on the SDU desulfurase activity as measured by sulfide production. Indeed, the removal of this zinc(II) ion from ISCU causes a moderate but significant increase in activity compared to SD alone, and FXN can activate both zinc-depleted and zinc-bound forms of ISCU complexed to SD. Recent yeast studies have reported a substitution on the yeast ISCU orthologue Isu, at position Met141 (Met140 in human numbering of precursor protein) to Ile, Leu, Val, or Cys that could bypass the requirement of FXN for Fe-S cluster assembly and cell viability. Using recombinant human proteins, we report no significant differences in the biochemical and biophysical properties observed between wild-type and variants M140I, M140 L, and M140 V of ISCU. Importantly, in the absence of FXN, ISCU variants behaved like wild-type and did not stimulate the desulfurase activity of the SD complex. This study therefore identifies an important regulatory role for ISCU-bound zinc in modulation of the human Fe-S assembly system in vitro but no ‘FXN bypass’ effect on mutations at position Met140 in human ISCU.ABBREVIATIONSACPacyl carrier transfer proteinBLIbiolayer interferometryBSAbovine serum albuminCDcircular dichroismDMPDNN-dimethyl-p-phenylenediamineDSFdifferential scanning fluorimetryDTTdithiothreitol; EDTA, ethylenediaminetetracetic acidFe-Siron sulfurFRDAFriedreich’s ataxiaFXNfrataxinHEPES4-(2-hydroxyethyl)-1-piperazineethanesulfonic acidIPTGisopropyl β-D-1-thiogalactopyranosidePLPpyridoxal 5′-phosphateSDprotein complex composed of NFS 1 and ISD11SDUprotein complex composed of NFS 1, ISD11ISCUSDUF, protein complex composed of NFS 1, ISD11, ISCU, and frataxinTCAtrichloroacetic acidTCEPtris(2-carboxyethyl) phosphineTristris(hydroxymethyl)aminomethane

scholarly journals Molecular Details of the Frataxin–Scaffold Interaction during Mitochondrial Fe–S Cluster Assembly

2021 ◽  
Vol 22 (11) ◽  
pp. 6006
Author(s):  
Courtney J. Campbell ◽  
Ashley E. Pall ◽  
Akshata R. Naik ◽  
Lindsey N. Thompson ◽  
Timothy L. Stemmler
Keyword(s):  
Acyl Carrier Protein ◽  
Model Systems ◽  
Cluster Assembly ◽  
Cysteine Desulfurase ◽  
Iron Sulfur Cluster ◽  
Iron Sulfur Clusters ◽  
Iron Sulfur ◽  
Entire Cell ◽  
Assembly Pathways ◽  
Insight Into

Iron–sulfur clusters are essential to almost every life form and utilized for their unique structural and redox-targeted activities within cells during many cellular pathways. Although there are three different Fe–S cluster assembly pathways in prokaryotes (the NIF, SUF and ISC pathways) and two in eukaryotes (CIA and ISC pathways), the iron–sulfur cluster (ISC) pathway serves as the central mechanism for providing 2Fe–2S clusters, directly and indirectly, throughout the entire cell in eukaryotes. Proteins central to the eukaryotic ISC cluster assembly complex include the cysteine desulfurase, a cysteine desulfurase accessory protein, the acyl carrier protein, the scaffold protein and frataxin (in humans, NFS1, ISD11, ACP, ISCU and FXN, respectively). Recent molecular details of this complex (labeled NIAUF from the first letter from each ISC protein outlined earlier), which exists as a dimeric pentamer, have provided real structural insight into how these partner proteins arrange themselves around the cysteine desulfurase, the core dimer of the (NIAUF)2 complex. In this review, we focus on both frataxin and the scaffold within the human, fly and yeast model systems to provide a better understanding of the biophysical characteristics of each protein alone and within the FXN/ISCU complex as it exists within the larger NIAUF construct. These details support a complex dynamic interaction between the FXN and ISCU proteins when both are part of the NIAUF complex and this provides additional insight into the coordinated mechanism of Fe–S cluster assembly.

scholarly journals The Iron-Sulfur Cluster Proteins Isa1 and Isa2 Are Required for the Function but Not for the De Novo Synthesis of the Fe/S Clusters of Biotin Synthase in Saccharomyces cerevisiae

2007 ◽  
Vol 6 (3) ◽  
pp. 495-504 ◽  
Author(s):  
Ulrich Mühlenhoff ◽  
Mathias J. Gerl ◽  
Birgit Flauger ◽  
Heike M. Pirner ◽  
Sandra Balser ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
De Novo ◽  
Mitochondrial Protein ◽  
Cluster Assembly ◽  
De Novo Synthesis ◽  
Biotin Synthase ◽  
Iron Sulfur Cluster ◽  
Iron Sulfur ◽  
Low Levels

ABSTRACT The yeast Saccharomyces cerevisiae is able to use some biotin precursors for biotin biosynthesis. Insertion of a sulfur atom into desthiobiotin, the final step in the biosynthetic pathway, is catalyzed by biotin synthase (Bio2). This mitochondrial protein contains two iron-sulfur (Fe/S) clusters that catalyze the reaction and are thought to act as a sulfur donor. To identify new components of biotin metabolism, we performed a genetic screen and found that Isa2, a mitochondrial protein involved in the formation of Fe/S proteins, is necessary for the conversion of desthiobiotin to biotin. Depletion of Isa2 or the related Isa1, however, did not prevent the de novo synthesis of any of the two Fe/S centers of Bio2. In contrast, Fe/S cluster assembly on Bio2 strongly depended on the Isu1 and Isu2 proteins. Both isa mutants contained low levels of Bio2. This phenotype was also found in other mutants impaired in mitochondrial Fe/S protein assembly and in wild-type cells grown under iron limitation. Low Bio2 levels, however, did not cause the inability of isa mutants to utilize desthiobiotin, since this defect was not cured by overexpression of BIO2. Thus, the Isa proteins are crucial for the in vivo function of biotin synthase but not for the de novo synthesis of its Fe/S clusters. Our data demonstrate that the Isa proteins are essential for the catalytic activity of Bio2 in vivo.

scholarly journals A Global Proteomic Approach Sheds New Light on Potential Iron-Sulfur Client Proteins of the Chloroplastic Maturation Factor NFU3

2020 ◽  
Vol 21 (21) ◽  
pp. 8121
Author(s):  
Nathalie Berger ◽  
Florence Vignols ◽  
Brigitte Touraine ◽  
Maël Taupin-Broggini ◽  
Valérie Rofidal ◽  
...  
Keyword(s):  
De Novo ◽  
Protein Localization ◽  
Expression Patterns ◽  
Specific Protein ◽  
Protein Accumulation ◽  
Loss Of Function ◽  
Iron Sulfur ◽  
Proteomic Approach ◽  
Client Proteins ◽  
S Proteins

Iron-sulfur (Fe-S) proteins play critical functions in plants. Most Fe-S proteins are synthetized in the cytosol as apo-proteins and the subsequent Fe-S cluster incorporation relies on specific protein assembly machineries. They are notably formed by a scaffold complex, which serves for the de novo Fe-S cluster synthesis, and by transfer proteins that insure cluster delivery to apo-targets. However, scarce information is available about the maturation pathways of most plastidial Fe-S proteins and their specificities towards transfer proteins of the associated SUF machinery. To gain more insights into these steps, the expression and protein localization of the NFU1, NFU2, and NFU3 transfer proteins were analyzed in various Arabidopsis thaliana organs and tissues showing quite similar expression patterns. In addition, quantitative proteomic analysis of an nfu3 loss-of-function mutant allowed to propose novel potential client proteins for NFU3 and to show that the protein accumulation profiles and thus metabolic adjustments differ substantially from those established in the nfu2 mutant. By clarifying the respective roles of the three plastidial NFU paralogs, these data allow better delineating the maturation process of plastidial Fe-S proteins.

scholarly journals Mitochondrial Fatty Acids and Neurodegenerative Disorders

2020 ◽  
pp. 107385842093616 ◽  
Author(s):  
Alexander J. Kastaniotis ◽  
Kaija J. Autio ◽  
Remya R. Nair
Keyword(s):  
Fatty Acids ◽  
De Novo ◽  
Acyl Carrier Protein ◽  
Acid Synthesis ◽  
Sensu Stricto ◽  
Common Symptom ◽  
Iron Sulfur Cluster ◽  
Iron Sulfur ◽  
Mitochondrial Fatty Acid ◽  
Oxidation Substrates

Fatty acids in mitochondria, in sensu stricto, arise either as β-oxidation substrates imported via the carnitine shuttle or through de novo synthesis by the mitochondrial fatty acid synthesis (mtFAS) pathway. Defects in mtFAS or processes involved in the generation of the mtFAS product derivative lipoic acid (LA), including iron-sulfur cluster synthesis required for functional LA synthase, have emerged only recently as etiology for neurodegenerative disease. Intriguingly, mtFAS deficiencies very specifically affect CNS function, while LA synthesis and attachment defects have a pleiotropic presentation beyond neurodegeneration. Typical mtFAS defect presentations include optical atrophy, as well as basal ganglia defects associated with dystonia. The phenotype display of patients with mtFAS defects can resemble the presentation of disorders associated with coenzyme A (CoA) synthesis. A recent publication links these processes together based on the requirement of CoA for acyl carrier protein maturation. MtFAS defects, CoA synthesis- as well as Fe-S cluster-deficiencies share lack of LA as a common symptom.

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