title: The ISC [corrected] 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.
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.
authors.affiliation: Institut für Zytobiologie und Zytopathologie, Philipps-Universität Marburg, Robert-Koch-Strasse 6, 35033 Marburg, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Mühlenhoff
authors.forename: Mathias J
authors.initials: MJ
authors.lastname: Gerl
authors.forename: Birgit
authors.initials: B
authors.lastname: Flauger
authors.forename: Heike M
authors.initials: HM
authors.lastname: Pirner
authors.forename: Sandra
authors.initials: S
authors.lastname: Balser
authors.forename: Nadine
authors.initials: N
authors.lastname: Richhardt
authors.forename: Roland
authors.initials: R
authors.lastname: Lill
authors.forename: Jürgen
authors.initials: J
authors.lastname: Stolz
mesh_terms: D053898:Biosynthetic Pathways; D001710:Biotin / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000096:biosynthesis / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000096:biosynthesis / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013466:Sulfurtransferases / Q000096:biosynthesis / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C410039:ISA1 protein, S cerevisiae; C410064:ISA2 protein, S cerevisiae; D007506:Iron-Sulfur Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D001710:Biotin; C004749:desthiobiotin; D013466:Sulfurtransferases; C057985:biotin synthetase