Architecture of the human mitochondrial iron-sulfur cluster assembly machinery

Research output: Contribution to journalArticle

Abstract

Fe-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 Escherichia coli the following 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 Å 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 12 [NFS1]2·[ISD11]2 sub-complexes to the surface results in a globular macromolecule with a 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.

Details

Authors
  • Oleksandr Gakh
  • Wasantha Ranatunga
  • Douglas Y. Smith
  • Eva Christina Ahlgren
  • Salam Al-Karadaghi
  • James R. Thompson
  • Grazia Isaya
Organisations
External organisations
  • Mayo Clinic Minnesota
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biochemistry and Molecular Biology
  • Other Basic Medicine
Original languageEnglish
Pages (from-to)21296-21321
Number of pages26
JournalJournal of Biological Chemistry
Volume291
Issue number40
Publication statusPublished - 2016 Sep 30
Publication categoryResearch
Peer-reviewedYes