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.
Iron-sulfur (Fe/S) proteins are involved in a wide variety of cellular processes such as enzymatic reactions, respiration, cofactor biosynthesis, ribosome biogenesis, regulation of gene expression, ...and DNA-RNA metabolism. Assembly of Fe/S clusters, small inorganic cofactors, is assisted by complex proteinaceous machineries, which use cysteine as a source of sulfur, combine it with iron to synthesize an Fe/S cluster on scaffold proteins, and finally incorporate the cluster into recipient apoproteins. In eukaryotes, such as yeast and human cells, more than 20 components are known that facilitate the maturation of Fe/S proteins in mitochondria, cytosol, and nucleus. These biogenesis components also perform crucial roles in other cellular pathways, e.g., in the regulation of iron homeostasis or the modification of tRNA. Numerous diseases including several neurodegenerative and hematological disorders have been associated with defects in Fe/S protein biogenesis, underlining the central importance of this process for life.
Mechanistic concepts of iron-sulfur protein biogenesis in Biology Braymer, Joseph J.; Freibert, Sven A.; Rakwalska-Bange, Magdalena ...
Biochimica et biophysica acta. Molecular cell research,
January 2021, 2021-01-00, 20210101, Letnik:
1868, Številka:
1
Journal Article
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Iron-sulfur (Fe/S) proteins are present in virtually all living organisms and are involved in numerous cellular processes such as respiration, photosynthesis, metabolic reactions, nitrogen fixation, ...radical biochemistry, protein synthesis, antiviral defense, and genome maintenance. Their versatile functions may go back to the proposed role of their Fe/S cofactors in the origin of life as efficient catalysts and electron carriers. More than two decades ago, it was discovered that the in vivo synthesis of cellular Fe/S clusters and their integration into polypeptide chains requires assistance by complex proteinaceous machineries, despite the fact that Fe/S proteins can be assembled chemically in vitro. In prokaryotes, three Fe/S protein biogenesis systems are known; ISC, SUF, and the more specialized NIF. The former two systems have been transferred by endosymbiosis from bacteria to mitochondria and plastids, respectively, of eukaryotes. In their cytosol, eukaryotes use the CIA machinery for the biogenesis of cytosolic and nuclear Fe/S proteins. Despite the structural diversity of the protein constituents of these four machineries, general mechanistic concepts underlie the complex process of Fe/S protein biogenesis. This review provides a comprehensive and comparative overview of the various known biogenesis systems in Biology, and summarizes their common or diverging molecular mechanisms, thereby illustrating both the conservation and diverse adaptions of these four machineries during evolution and under different lifestyles. Knowledge of these fundamental biochemical pathways is not only of basic scientific interest, but is important for the understanding of human ‘Fe/S diseases’ and can be used in biotechnology.
•FeS proteins assist numerous cellular processes and many are essential for life.•FeS proteins are assembled by one or more out of four different machineries.•Similar mechanistic concepts underlie FeS protein biogenesis in all machineries.•Biogenesis involves synthesis, trafficking and apoprotein targeting of FeS clusters.•Minimal machineries reveal the basic biochemical requirements for biogenesis.
The yeast mitochondrial ABC transporter Atm1, in concert with glutathione, functions in the export of a substrate required for cytosolic-nuclear iron-sulfur protein biogenesis and cellular iron ...regulation. Defects in the human ortholog ABCB7 cause the sideroblastic anemia XLSA/A. Here, we report the crystal structures of free and glutathione-bound Atm1 in inward-facing, open conformations at 3.06- and 3.38-angstrom resolution, respectively. The glutathione binding site includes a residue mutated in XLSA/A and is located close to the inner membrane surface in a large cavity. The two nucleotide-free adenosine 5'-triphosphate binding domains do not interact yet are kept in close vicinity through tight interaction of the two C-terminal α-helices of the Atm1 dimer. The resulting protein stabilization may be a common structural feature of all ABC exporters.
Metabolism controls gene expression through allosteric interactions between metabolites and transcription factors. These interactions are usually measured with in vitro assays, but there are no ...methods to identify them at a genome-scale in vivo. Here we show that dynamic transcriptome and metabolome data identify metabolites that control transcription factors in E. coli. By switching an E. coli culture between starvation and growth, we induce strong metabolite concentration changes and gene expression changes. Using Network Component Analysis we calculate the activities of 209 transcriptional regulators and correlate them with metabolites. This approach captures, for instance, the in vivo kinetics of CRP regulation by cyclic-AMP. By testing correlations between all pairs of transcription factors and metabolites, we predict putative effectors of 71 transcription factors, and validate five interactions in vitro. These results show that combining transcriptomics and metabolomics generates hypotheses about metabolism-transcription interactions that drive transitions between physiological states.
Iron-sulfur (Fe/S) clusters require a complex set of proteins to become assembled and incorporated into apoproteins in a living cell. Researchers have described three distinct assembly systems in ...eukaryotes that are involved in the maturation of cellular Fe/S proteins. Mitochondria are central for biogenesis. They contain the ISC-the iron-sulfur cluster assembly machinery that was inherited from a similar system of eubacteria in evolution and is involved in biogenesis of all cellular Fe/S proteins. The basic principle of mitochondrial (and bacterial) Fe/S protein maturation is the synthesis of the Fe/S cluster on a scaffold protein before the cluster is transferred to apoproteins. Biogenesis of cytosolic and nuclear Fe/S proteins is facilitated by the cytosolic iron-sulfur protein assembly (CIA) apparatus. This process requires the participation of mitochondria that export a still unknown component via the ISC export machinery, including an ABC transporter.
Iron-sulfur (Fe/S) clusters are essential protein cofactors crucial for many cellular functions including DNA maintenance, protein translation, and energy conversion. De novo Fe/S cluster synthesis ...occurs on the mitochondrial scaffold protein ISCU and requires cysteine desulfurase NFS1, ferredoxin, frataxin, and the small factors ISD11 and ACP (acyl carrier protein). Both the mechanism of Fe/S cluster synthesis and function of ISD11-ACP are poorly understood. Here, we present crystal structures of three different NFS1-ISD11-ACP complexes with and without ISCU, and we use SAXS analyses to define the 3D architecture of the complete mitochondrial Fe/S cluster biosynthetic complex. Our structural and biochemical studies provide mechanistic insights into Fe/S cluster synthesis at the catalytic center defined by the active-site Cys of NFS1 and conserved Cys, Asp, and His residues of ISCU. We assign specific regulatory rather than catalytic roles to ISD11-ACP that link Fe/S cluster synthesis with mitochondrial lipid synthesis and cellular energy status.
Iron-sulphur (Fe-S) clusters have long been recognized as essential and versatile cofactors of proteins involved in catalysis, electron transport and sensing of ambient conditions. Despite the ...relative simplicity of Fe-S clusters in terms of structure and composition, their synthesis and assembly into apoproteins is a highly complex and coordinated process in living cells. Different biogenesis machineries in both bacteria and eukaryotes have been discovered that assist Fe-S-protein maturation according to uniform biosynthetic principles. The importance of Fe-S proteins for life is documented by an increasing number of diseases linked to these components and their biogenesis.
The essential process of iron-sulfur (Fe/S) cluster assembly (ISC) in mitochondria occurs in three major phases. First, 2Fe-2S clusters are synthesized on the scaffold protein ISCU2; second, these ...clusters are transferred to the monothiol glutaredoxin GLRX5 by an Hsp70 system followed by insertion into 2Fe-2S apoproteins; third, 4Fe-4S clusters are formed involving the ISC proteins ISCA1–ISCA2–IBA57 followed by target-specific apoprotein insertion. The third phase is poorly characterized biochemically, because previous in vitro assembly reactions involved artificial reductants and lacked at least one of the in vivo-identified ISC components. Here, we reconstituted the maturation of mitochondrial 4Fe-4S aconitase without artificial reductants and verified the 2Fe-2S-containing GLRX5 as cluster donor. The process required all components known from in vivo studies (i.e., ISCA1–ISCA2–IBA57), yet surprisingly also depended on mitochondrial ferredoxin FDX2 and its NADPH-coupled reductase FDXR. Electrons from FDX2 catalyze the reductive 2Fe-2S cluster fusion on ISCA1–ISCA2 in an IBA57-dependent fashion. This previously unidentified electron transfer was occluded during previous in vivo studies due to the earlier FDX2 requirement for 2Fe-2S cluster synthesis on ISCU2. The FDX2 function is specific, because neither FDX1, a mitochondrial ferredoxin involved in steroid production, nor other cellular reducing systems, supported maturation. In contrast to ISC factorassisted 4Fe-4S protein assembly, 2Fe-2S cluster transfer from GLRX5 to 2Fe-2S apoproteins occurred spontaneously within seconds, clearly distinguishing the mechanisms of 2Fe-2S and 4Fe-4S protein maturation. Our study defines the physiologically relevant mechanistic action of late-acting ISC factors in mitochondrial 4Fe-4S cluster synthesis, trafficking, and apoprotein insertion.
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![Mitochondrial [4Fe-4S] prot...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0027-8424_1091-6490/small "Mitochondrial [4Fe-4S] protein assembly involves reductive [2Fe-2S] cluster fusion on ISCA1–ISCA2 by electron flow from ferredoxin FDX2")