title: The Human Iron-Sulfur Assembly Complex Catalyzes the Synthesis of [2Fe-2S] Clusters on ISCU2 That Can Be Transferred to Acceptor Molecules.
abstract: Iron-sulfur (Fe-S) clusters are essential protein cofactors for most life forms. In human mitochondria, the core Fe-S biosynthetic enzymatic complex (called SDUF) consists of NFS1, ISD11, ISCU2, and frataxin (FXN) protein components. Few mechanistic details about how this complex synthesizes Fe-S clusters and how these clusters are delivered to targets are known. Here circular dichroism and Mössbauer spectroscopies were used to reveal details of the Fe-S cluster assembly reaction on the SDUF complex. SDUF reactions generated [2Fe-2S] cluster intermediates that readily converted to stable [2Fe-2S] clusters bound to uncomplexed ISCU2. Similar reactions that included the apo Fe-S acceptor protein human ferredoxin (FDX1) resulted in formation of [2Fe-2S]-ISCU2 rather than [2Fe-2S]-FDX1. Subsequent addition of dithiothreitol (DTT) induced transfer of the cluster from ISCU2 to FDX1, suggesting that [2Fe-2S]-ISCU2 is an intermediate. Reactions that initially included DTT rapidly generated [2Fe-2S]-FDX1 and bypassed formation of [2Fe-2S]-ISCU2. In the absence of apo-FDX1, incubation of [2Fe-2S]-ISCU2 with DTT generated [4Fe-4S]-ISCU2 species. Together, these results conflict with a recent report of stable [4Fe-4S] cluster formation on the SDUF complex. Rather, they support a model in which SDUF builds transient [2Fe-2S] cluster intermediates that generate clusters on sulfur-containing molecules, including uncomplexed ISCU2. Additional small molecule or protein factors are required for the transfer of these clusters to Fe-S acceptor proteins or the synthesis of [4Fe-4S] clusters.
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Fox
authors.forename: Mrinmoy
authors.initials: M
authors.lastname: Chakrabarti
authors.forename: Sean P
authors.initials: SP
authors.lastname: McCormick
authors.forename: Paul A
authors.initials: PA
authors.lastname: Lindahl
authors.forename: David P
authors.initials: DP
authors.lastname: Barondeau
mesh_terms: D055162:Biocatalysis; D013437:Carbon-Sulfur Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002942:Circular Dichroism; D006801:Humans; D007501:Iron / Q000378:metabolism; D033862:Iron-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D035925:Iron-Regulatory Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D013455:Sulfur / Q000378:metabolism; D000096923:Frataxin
chemical_list: D013437:Carbon-Sulfur Lyases; D007501:Iron; D033862:Iron-Binding Proteins; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D013455:Sulfur; D000096923:Frataxin; C506160:ISCU protein, human; C544445:LYRM4 protein, human; C513492:NFS1 protein, human