5kz5
From Proteopedia
Architecture of the Human Mitochondrial Iron-Sulfur Cluster Assembly Machinery: the Complex Formed by the Iron Donor, the Sulfur Donor, and the Scaffold
Structural highlights
Disease[NFS1_HUMAN] Severe neonatal lactic acidosis due to NFS1-ISD11 complex deficiency. [ISCU_HUMAN] Hereditary myopathy with lactic acidosis due to ISCU deficiency. The disease is caused by mutations affecting the gene represented in this entry. [FRDA_HUMAN] Defects in FXN are the cause of Friedreich ataxia (FRDA) [MIM:229300]. FRDA is an autosomal recessive, progressive degenerative disease characterized by neurodegeneration and cardiomyopathy it is the most common inherited ataxia. The disorder is usually manifest before adolescence and is generally characterized by incoordination of limb movements, dysarthria, nystagmus, diminished or absent tendon reflexes, Babinski sign, impairment of position and vibratory senses, scoliosis, pes cavus, and hammer toe. In most patients, FRDA is due to GAA triplet repeat expansions in the first intron of the frataxin gene. But in some cases the disease is due to mutations in the coding region.[:][:][1] [2] [3] [4] [:][5] [6] Function[NFS1_HUMAN] Catalyzes the removal of elemental sulfur from cysteine to produce alanine. It supplies the inorganic sulfur for iron-sulfur (Fe-S) clusters. May be involved in the biosynthesis of molybdenum cofactor.[7] [ISCU_HUMAN] Scaffold protein for the de novo synthesis of iron-sulfur (Fe-S) clusters within mitochondria, which is required for maturation of both mitochondrial and cytoplasmic [2Fe-2S] and [4Fe-4S] proteins (PubMed:11060020). First, a [2Fe-2S] cluster is transiently assembled on the scaffold protein ISCU. In a second step, the cluster is released from ISCU, transferred to a glutaredoxin GLRX5, followed by the formation of mitochondrial [2Fe-2S] proteins, the synthesis of [4Fe-4S] clusters and their target-specific insertion into the recipient apoproteins. Cluster assembly on ISCU depends on the function of the cysteine desulfurase complex NFS1-LYRM4/ISD11, which serves as the sulfur donor for cluster synthesis, the iron-binding protein frataxin as the putative iron donor, and the electron transfer chain comprised of ferredoxin reductase and ferredoxin, which receive their electrons from NADH (By similarity).[UniProtKB:Q03020][8] [FRDA_HUMAN] Promotes the biosynthesis of heme and assembly and repair of iron-sulfur clusters by delivering Fe(2+) to proteins involved in these pathways. May play a role in the protection against iron-catalyzed oxidative stress through its ability to catalyze the oxidation of Fe(2+) to Fe(3+); the oligomeric form but not the monomeric form has in vitro ferroxidase activity. May be able to store large amounts of iron in the form of a ferrihydrite mineral by oligomerization; however, the physiological relevance is unsure as reports are conflicting and the function has only been shown using heterologous overexpression systems. Modulates the RNA-binding activity of ACO1.[9] [10] [11] [12] [13] [14] [15] [16] [17] Publication Abstract from PubMedFe-S clusters, essential cofactors needed for the activity of many different enzymes, are assembled by conserved protein machineries inside bacteria and mitochondria. As the architecture of the human machinery remains undefined, we co-expressed in E. coli four proteins involved in the initial step of Fe-S cluster synthesis: FXN42-210 (iron donor), [NFS1]-[ISD11] (sulfur donor), and ISCU (scaffold upon which new clusters are assembled). We purified a stable, active complex consisting of all four proteins with 1:1:1:1 stoichiometry. Using negative staining transmission EM and single particle analysis, we obtained a three-dimensional model of the complex with ~14 A resolution. Molecular dynamics flexible fitting of protein structures docked into the EM map of the model revealed a [FXN42-210]24-[NFS1]24-[ISD11]24-[ISCU]24, complex, consistent with the measured 1:1:1:1 stoichiometry of its four components. The complex structure fulfills distance constraints obtained from chemical cross-linking of the complex at multiple recurring interfaces, involving hydrogen bonds, salt bridges or hydrophobic interactions between conserved residues. The complex consists of a central, roughly cubic [FXN42-210]24-[ISCU]24 sub-complex with one symmetric ISCU trimer bound on top of one symmetric FXN42-210 trimer at each of its eight vertices. Binding of twelve [NFS1]2-[ISD11]2 sub-complexes to the surface results in a globular macromolecule with diameter of ~15 nm, and creates 24 Fe-S cluster assembly centers. The organization of each center recapitulates a previously proposed, conserved mechanism for sulfur donation from NFS1 to ISCU and reveals - for the first time - a path for iron donation from FXN42-210 to ISCU. Architecture of the Human Mitochondrial Iron-Sulfur Cluster Assembly Machinery.,Gakh O, Ranatunga W, Smith DY 4th, Ahlgren EC, Al-Karadaghi S, Thompson JR, Isaya G J Biol Chem. 2016 Aug 12. pii: jbc.M116.738542. PMID:27519411[18] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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