{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,6]],"date-time":"2026-10-06T14:05:52Z","timestamp":1791295552411,"version":"4.1.0"},"reference-count":44,"publisher":"American Chemical Society (ACS)","issue":"30","license":[{"start":{"date-parts":[[2015,6,27]],"date-time":"2015-06-27T00:00:00Z","timestamp":1435363200000},"content-version":"vor","delay-in-days":365,"URL":"https:\/\/pubs.acs.org\/page\/policy\/authorchoice_termsofuse.html"}],"funder":[{"DOI":"10.13039\/100000057","name":"National Institute of General Medical Sciences","doi-asserted-by":"publisher","award":["GM096100"],"award-info":[{"award-number":["GM096100"]}],"id":[{"id":"10.13039\/100000057","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/100000928","name":"Welch Foundation","doi-asserted-by":"publisher","award":["A-1647"],"award-info":[{"award-number":["A-1647"]}],"id":[{"id":"10.13039\/100000928","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2014,8,5]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Iron\u2013sulfur clusters are ubiquitous protein cofactors with critical cellular functions. The mitochondrial Fe\u2013S assembly complex, which consists of the cysteine desulfurase NFS1 and its accessory protein (ISD11), the Fe\u2013S assembly protein (ISCU2), and frataxin (FXN), converts substrates l-cysteine, ferrous iron, and electrons into Fe\u2013S clusters. The physiological function of FXN has received a tremendous amount of attention since the discovery that its loss is directly linked to the neurodegenerative disease Friedreich\u2019s ataxia. Previous in vitro results revealed a role for human FXN in activating the cysteine desulfurase and Fe\u2013S cluster biosynthesis activities of the Fe\u2013S assembly complex. Here we present radiolabeling experiments that indicate FXN accelerates the accumulation of sulfur on ISCU2 and that the resulting persulfide species is viable in the subsequent synthesis of Fe\u2013S clusters. Additional mutagenesis, enzyme kinetic, UV\u2013visible, and circular dichroism spectroscopic studies suggest conserved ISCU2 residue C104 is critical for FXN activation, whereas C35, C61, and C104 are all essential for Fe\u2013S cluster formation on the assembly complex. These results cannot be fully explained by the hypothesis that FXN functions as an iron donor for Fe\u2013S cluster biosynthesis, and further support an allosteric regulator role for FXN. Together, these results lead to an activation model in which FXN accelerates persulfide formation on NFS1 and favors a helix-to-coil interconversion on ISCU2 that facilitates the transfer of sulfur from NFS1 to ISCU2 as an initial step in Fe\u2013S cluster biosynthesis.<\/jats:p>","DOI":"10.1021\/bi500532e","type":"journal-article","created":{"date-parts":[[2014,6,27]],"date-time":"2014-06-27T12:06:40Z","timestamp":1403870800000},"page":"4904-4913","source":"Crossref","is-referenced-by-count":160,"title":["Human Frataxin Activates Fe\u2013S Cluster Biosynthesis\nby Facilitating Sulfur Transfer Chemistry"],"prefix":"10.1021","volume":"53","author":[{"given":"Jennifer","family":"Bridwell-Rabb","sequence":"first","affiliation":[{"name":"Texas A&M University , , , ,","place":["College Station, Texas, United States, 77842"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nicholas G.","family":"Fox","sequence":"additional","affiliation":[{"name":"Texas A&M University , , , ,","place":["College Station, Texas, United States, 77842"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chi-Lin","family":"Tsai","sequence":"additional","affiliation":[{"name":"Texas A&M University , , , ,","place":["College Station, Texas, United States, 77842"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Andrew M.","family":"Winn","sequence":"additional","affiliation":[{"name":"Texas A&M University , , , ,","place":["College Station, Texas, United States, 77842"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"David P.","family":"Barondeau","sequence":"additional","affiliation":[{"name":"Texas A&M University , , , ,","place":["College Station, Texas, United States, 77842"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"316","published-online":{"date-parts":[[2014,6,27]]},"reference":[{"key":"2026090120154085900_cit1","doi-asserted-by":"crossref","first-page":"825","DOI":"10.1111\/j.1574-6976.2006.00036.x","article-title":"Enzymatic\nactivation of sulfur for incorporation into biomolecules in prokaryotes","volume":"30","author":"Kessler","year":"2006","journal-title":"FEMS Microbiol. Rev."},{"key":"2026090120154085900_cit2","doi-asserted-by":"crossref","first-page":"185","DOI":"10.1038\/nchembio779","article-title":"Trafficking\nin persulfides: Delivering sulfur in biosynthetic pathways","volume":"2","author":"Mueller","year":"2006","journal-title":"Nat. Chem. Biol."},{"key":"2026090120154085900_cit3","doi-asserted-by":"crossref","first-page":"4714","DOI":"10.1021\/bi00181a031","article-title":"Mechanism for the\ndesulfurization of l-cysteine catalyzed by the nifS gene\nproduct","volume":"33","author":"Zheng","year":"1994","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit4","doi-asserted-by":"crossref","first-page":"12220","DOI":"10.1021\/bi049143e","article-title":"Mechanism\nof cysteine desulfurase\nSlr0387 from Synechocystis sp. PCC\n6803: Kinetic analysis of cleavage of the persulfide intermediate\nby chemical reductants","volume":"43","author":"Behshad","year":"2004","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit5","doi-asserted-by":"crossref","first-page":"1049","DOI":"10.1016\/S0022-2836(03)00690-9","article-title":"Crystal structure\nof IscS, a cysteine\ndesulfurase from Escherichia coli","volume":"330","author":"Cupp-Vickery","year":"2003","journal-title":"J. Mol. Biol."},{"key":"2026090120154085900_cit6","doi-asserted-by":"crossref","first-page":"44521","DOI":"10.1074\/jbc.M106907200","article-title":"Transfer of sulfur\nfrom IscS to IscU during Fe\/S cluster assembly","volume":"276","author":"Urbina","year":"2001","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit7","doi-asserted-by":"crossref","first-page":"11103","DOI":"10.1021\/ja016757n","article-title":"Sulfur transfer from IscS to IscU:\nThe first step in iron-sulfur cluster biosynthesis","volume":"123","author":"Smith","year":"2001","journal-title":"J. Am. Chem. Soc."},{"key":"2026090120154085900_cit8","doi-asserted-by":"crossref","first-page":"5236","DOI":"10.1016\/j.febslet.2005.08.046","article-title":"Role of conserved cysteines\nin mediating sulfur transfer from IscS to IscU","volume":"579","author":"Smith","year":"2005","journal-title":"FEBS Lett."},{"key":"2026090120154085900_cit9","doi-asserted-by":"crossref","first-page":"5439","DOI":"10.1002\/anie.201201708","article-title":"(IscS-IscU)2 complex structures\nprovide insights into Fe2S2 biogenesis and transfer","volume":"51","author":"Marinoni","year":"2012","journal-title":"Angew. Chem., Int. Ed."},{"key":"2026090120154085900_cit10","doi-asserted-by":"crossref","first-page":"e1000354","DOI":"10.1371\/journal.pbio.1000354","article-title":"Structural basis for\nFe-S cluster assembly and tRNA\nthiolation mediated by IscS protein-protein interactions","volume":"8","author":"Shi","year":"2010","journal-title":"PLoS Biol."},{"key":"2026090120154085900_cit11","doi-asserted-by":"crossref","first-page":"5948","DOI":"10.1073\/pnas.082123599","article-title":"Cys-328 of IscS and\nCys-63 of IscU are the sites of disulfide bridge formation in a covalently\nbound IscS\/IscU complex: Implications for the mechanism of iron-sulfur\ncluster assembly","volume":"99","author":"Kato","year":"2002","journal-title":"Proc. Natl. Acad. Sci. U.S.A."},{"key":"2026090120154085900_cit12","doi-asserted-by":"crossref","first-page":"2506","DOI":"10.1021\/bi201628j","article-title":"Effector\nrole reversal during evolution: The case of frataxin in Fe-S cluster\nbiosynthesis","volume":"51","author":"Bridwell-Rabb","year":"2012","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit13","doi-asserted-by":"crossref","first-page":"e21992","DOI":"10.1371\/journal.pone.0021992","article-title":"The Role of CyaY in Iron Sulfur Cluster Assembly on\nthe E. coli IscU Scaffold Protein","volume":"6","author":"Iannuzzi","year":"2011","journal-title":"PLoS One"},{"key":"2026090120154085900_cit14","doi-asserted-by":"crossref","first-page":"9641","DOI":"10.1021\/bi201123z","article-title":"Facilitated\ntransfer of IscU-[2Fe2S] clusters by chaperone-mediated ligand exchange","volume":"50","author":"Bonomi","year":"2011","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit15","doi-asserted-by":"crossref","first-page":"9132","DOI":"10.1021\/bi1013062","article-title":"Human frataxin is an allosteric switch that activates\nthe Fe-S cluster biosynthetic complex","volume":"49","author":"Tsai","year":"2010","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit16","doi-asserted-by":"crossref","first-page":"e16199","DOI":"10.1371\/journal.pone.0016199","article-title":"Mammalian Frataxin: An Essential\nFunction for Cellular Viability through an Interaction with a Preformed\nISCU\/NFS1\/ISD11 Iron-Sulfur Assembly Complex","volume":"6","author":"Schmucker","year":"2011","journal-title":"PLoS One"},{"key":"2026090120154085900_cit17","doi-asserted-by":"crossref","first-page":"2754","DOI":"10.1073\/pnas.90.7.2754","article-title":"Cysteine\ndesulfurase activity indicates a role for NIFS in metallocluster biosynthesis","volume":"90","author":"Zheng","year":"1993","journal-title":"Proc. Natl. Acad. Sci. U.S.A."},{"key":"2026090120154085900_cit18","doi-asserted-by":"crossref","first-page":"174","DOI":"10.1038\/sj.emboj.7600905","article-title":"The Nfs1 interacting\nprotein Isd11 has an essential role in Fe\/S cluster biogenesis in\nmitochondria","volume":"25","author":"Adam","year":"2006","journal-title":"EMBO J."},{"key":"2026090120154085900_cit19","doi-asserted-by":"crossref","first-page":"929","DOI":"10.1093\/hmg\/ddm038","article-title":"Mitochondrial\nfrataxin interacts\nwith ISD11 of the NFS1\/ISCU complex and multiple mitochondrial chaperones","volume":"16","author":"Shan","year":"2007","journal-title":"Hum. Mol. Genet."},{"key":"2026090120154085900_cit20","doi-asserted-by":"crossref","first-page":"3014","DOI":"10.1093\/hmg\/ddp239","article-title":"Human ISD11 is essential\nfor both iron-sulfur cluster assembly and maintenance of normal cellular\niron homeostasis","volume":"18","author":"Shi","year":"2009","journal-title":"Hum. Mol. Genet."},{"key":"2026090120154085900_cit21","doi-asserted-by":"crossref","first-page":"184","DOI":"10.1038\/sj.emboj.7600906","article-title":"Essential\nrole of Isd11\nin mitochondrial iron-sulfur cluster synthesis on Isu scaffold proteins","volume":"25","author":"Wiedemann","year":"2006","journal-title":"EMBO J."},{"key":"2026090120154085900_cit22","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1042\/BJ20120951","article-title":"Persulfide\nformation on mitochondrial cysteine desulfurase: Enzyme activation\nby a eukaryote-specific interacting protein and Fe-S cluster synthesis","volume":"448","author":"Pandey","year":"2012","journal-title":"Biochem. J."},{"key":"2026090120154085900_cit23","doi-asserted-by":"crossref","first-page":"539","DOI":"10.1016\/j.mito.2012.07.103","article-title":"Identification\nof a Nfs1p-bound persulfide intermediate in Fe-S cluster synthesis\nby intact mitochondria","volume":"12","author":"Pandey","year":"2012","journal-title":"Mitochondrion"},{"key":"2026090120154085900_cit24","doi-asserted-by":"crossref","first-page":"6478","DOI":"10.1021\/bi200666h","article-title":"Friedreich\u2019s Ataxia Variants\nI154F and W155R Diminish Frataxin-Based Activation of the Iron-Sulfur\nCluster Assembly Complex","volume":"50","author":"Tsai","year":"2011","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit25","doi-asserted-by":"crossref","first-page":"7265","DOI":"10.1021\/bi200895k","article-title":"Structure-function\nanalysis of Friedreich\u2019s\nataxia mutants reveals determinants for frataxin binding and activation\nof the Fe-S assembly complex","volume":"50","author":"Bridwell-Rabb","year":"2011","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit26","doi-asserted-by":"crossref","first-page":"733","DOI":"10.1021\/ja308736e","article-title":"Mammalian\nFrataxin Controls Sulfur\nProduction and Iron Entry during de Novo Fe4S4 Cluster Assembly","volume":"135","author":"Colin","year":"2013","journal-title":"J. Am. Chem. Soc."},{"key":"2026090120154085900_cit27","doi-asserted-by":"crossref","first-page":"1423","DOI":"10.1126\/science.271.5254.1423","article-title":"Friedreich\u2019s\nataxia: Autosomal recessive disease caused by an intronic GAA triplet\nrepeat expansion","volume":"271","author":"Campuzano","year":"1996","journal-title":"Science"},{"key":"2026090120154085900_cit28","doi-asserted-by":"crossref","first-page":"e1","DOI":"10.1042\/BJ20091959","article-title":"Frataxin, a molecule of mystery:\nTrading stability for function in its iron-binding site","volume":"426","author":"Lane","year":"2010","journal-title":"Biochem. J."},{"key":"2026090120154085900_cit29","doi-asserted-by":"crossref","first-page":"9488","DOI":"10.1021\/bi960467f","article-title":"Human ferredoxin:\nOverproduction in Escherichia coli,\nreconstitution in vitro, and spectroscopic studies of iron-sulfur\ncluster ligand cysteine-to-serine mutants","volume":"35","author":"Xia","year":"1996","journal-title":"Biochemistry"},{"key":"2026090120154085900_cit30","doi-asserted-by":"crossref","first-page":"29513","DOI":"10.1074\/jbc.M504344200","article-title":"Multiple turnover transfer\nof [2Fe2S] clusters by the iron-sulfur cluster assembly scaffold proteins\nIscU and IscA","volume":"280","author":"Bonomi","year":"2005","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit31","doi-asserted-by":"crossref","first-page":"25178","DOI":"10.1074\/jbc.M804064200","article-title":"A novel role\nfor human Nfs1 in the cytoplasm: Nfs1 acts as a sulfur donor for MOCS3,\na protein involved in molybdenum cofactor biosynthesis","volume":"283","author":"Marelja","year":"2008","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit32","doi-asserted-by":"crossref","first-page":"126","DOI":"10.1016\/0003-2697(65)90051-5","article-title":"A direct\nmicrodetermination for sulfide","volume":"11","author":"Siegel","year":"1965","journal-title":"Anal. Biochem."},{"key":"2026090120154085900_cit33","doi-asserted-by":"crossref","first-page":"713","DOI":"10.1007\/s00775-005-0025-1","article-title":"Mechanisms of iron-sulfur\ncluster assembly: The SUF machinery","volume":"10","author":"Fontecave","year":"2005","journal-title":"JBIC, J.\nBiol. Inorg. Chem."},{"key":"2026090120154085900_cit34","doi-asserted-by":"crossref","first-page":"8117","DOI":"10.1021\/ja401950a","article-title":"[2Fe-2S]-Ferredoxin\nbinds directly to cysteine desulfurase and supplies an electron for\niron-sulfur cluster assembly but is displaced by the scaffold protein\nor bacterial frataxin","volume":"135","author":"Kim","year":"2013","journal-title":"J. Am. Chem. Soc."},{"key":"2026090120154085900_cit35","doi-asserted-by":"crossref","first-page":"16068","DOI":"10.1016\/S0021-9258(18)48580-8","article-title":"Escherichia coli contains a protein that is homologous\nin function and N-terminal sequence to the protein encoded by the\nnifS gene of Azotobacter vinelandii and that can participate in the synthesis of the Fe-S cluster of\ndihydroxy-acid dehydratase","volume":"271","author":"Flint","year":"1996","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit36","doi-asserted-by":"crossref","first-page":"21397","DOI":"10.1074\/jbc.M201439200","article-title":"Iron-sulfur cluster biosynthesis. Thermatoga maritima IscU is a structured iron-sulfur\ncluster assembly protein","volume":"277","author":"Mansy","year":"2002","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit37","doi-asserted-by":"crossref","first-page":"875","DOI":"10.1002\/prot.20421","article-title":"Structural characterization of an iron-sulfur cluster\nassembly protein IscU in a zinc-bound form","volume":"59","author":"Liu","year":"2005","journal-title":"Proteins"},{"key":"2026090120154085900_cit38","doi-asserted-by":"crossref","first-page":"567","DOI":"10.1016\/j.jmb.2004.08.038","article-title":"Solution NMR structure of the iron-sulfur\ncluster assembly protein U (IscU) with zinc bound at the active site","volume":"344","author":"Ramelot","year":"2004","journal-title":"J. Mol. Biol."},{"key":"2026090120154085900_cit39","doi-asserted-by":"crossref","first-page":"7933","DOI":"10.1021\/ja501260h","article-title":"Role of\nIscX in Iron-Sulfur Cluster Biogenesis in Escherichia coli","volume":"136","author":"Kim","year":"2014","journal-title":"J. Am. Chem. Soc."},{"key":"2026090120154085900_cit40","doi-asserted-by":"crossref","first-page":"653","DOI":"10.1126\/science.277.5326.653","article-title":"Iron-sulfur\nclusters: Nature\u2019s\nmodular, multipurpose structures","volume":"277","author":"Beinert","year":"1997","journal-title":"Science"},{"key":"2026090120154085900_cit41","doi-asserted-by":"crossref","first-page":"36773","DOI":"10.1074\/jbc.M113.525857","article-title":"Frataxin Directly Stimulates\nMitochondrial Cysteine Desulfurase by\nExposing Substrate-binding Sites, and a Mutant Fe-S Cluster Scaffold\nProtein with Frataxin-bypassing Ability Acts Similarly","volume":"288","author":"Pandey","year":"2013","journal-title":"J. Biol. Chem."},{"key":"2026090120154085900_cit42","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1016\/j.jmb.2008.08.015","article-title":"The Asymmetric\nTrimeric Architecture of [2Fe-2S] IscU: Implications for Its Scaffolding\nduring Iron-Sulfur Cluster Biosynthesis","volume":"383","author":"Shimomura","year":"2008","journal-title":"J.\nMol. Biol."},{"key":"2026090120154085900_cit43","doi-asserted-by":"crossref","first-page":"454","DOI":"10.1073\/pnas.1114372109","article-title":"Disordered\nform of the scaffold protein\nIscU is the substrate for iron-sulfur cluster assembly on cysteine\ndesulfurase","volume":"109","author":"Kim","year":"2012","journal-title":"Proc. Natl. Acad. Sci. U.S.A."},{"key":"2026090120154085900_cit44","doi-asserted-by":"crossref","first-page":"9595","DOI":"10.1021\/bi301413y","article-title":"Metamorphic\nProtein IscU Changes\nConformation by cis-trans Isomerizations of Two Peptidyl-Prolyl Peptide\nBonds","volume":"51","author":"Dai","year":"2012","journal-title":"Biochemistry"}],"container-title":["Biochemistry"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/bi500532e","content-type":"application\/pdf","content-version":"vor","intended-application":"unspecified"},{"URL":"https:\/\/pubs.acs.org\/bichaw\/article-pdf\/53\/30\/4904\/7873201\/bi500532e.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/pubs.acs.org\/bichaw\/article-pdf\/53\/30\/4904\/7873201\/bi500532e.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,2]],"date-time":"2026-09-02T00:15:52Z","timestamp":1788308152000},"score":1,"resource":{"primary":{"URL":"https:\/\/pubs.acs.org\/bichaw\/article\/53\/30\/4904\/772838\/Human-Frataxin-Activates-Fe-S-Cluster-Biosynthesis"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2014,6,27]]},"references-count":44,"journal-issue":{"issue":"30","published-online":{"date-parts":[[2014,6,27]]},"published-print":{"date-parts":[[2014,8,5]]}},"URL":"https:\/\/doi.org\/10.1021\/bi500532e","relation":{},"ISSN":["0006-2960","1520-4995"],"issn-type":[{"value":"0006-2960","type":"print"},{"value":"1520-4995","type":"electronic"}],"subject":[],"published":{"date-parts":[[2014,6,27]]}}}