Iron-sulfur cluster biosynthesis: functional characterization of the N- and C-terminal domains of human NFU

Biochemistry. 2009 Feb 10;48(5):973-80. doi: 10.1021/bi801645z.


Human NFU (also known as HIRIP5) has been implicated in cellular iron-sulfur cluster biosynthesis. Bacterial and yeast forms are smaller than the human protein and are homologous to the C-terminal domain of the latter. This C-terminal domain contains a pair of redox active cysteines and demonstrates thioredoxin-like activity by mediating persulfide bond cleavage of sulfur-loaded NifS (an IscS-type protein), the sulfide donor for [2Fe-2S] cluster assembly on ISU-type scaffold proteins. Herein, the affinity of full-length human NFU and the individual N- and C-terminal domains for sulfide donor and cluster scaffold proteins is assessed. The influence of the N-terminal domain on C-terminal NFU binding to NifS and persulfide reductase activity is also examined. Only the C-terminal domain is required for persulfide reductase activity, while complex formation of NifS with full-length NFU is similar to that of the C-terminal domain alone (K(D) approximately 9.7 +/- 0.7 and 10.1 +/- 0.6 microM, respectively). There is negligible affinity between the isolated C- and N-terminal domains, while the N-terminal domain has negligible affinity for either sulfide donor or cluster scaffold proteins. The temperature dependence of the binding enthalpy for formation of the complex between NifS and the C-terminal domain of NFU yields a change in molar heat capacity (DeltaC(p) approximately 138 cal mol(-1) K(-1)) that suggests bonding at the protein-protein interface is dominated by electrostatic interactions. This is consistent with electrostatic potential maps for bacterial homologues of the N- and C-terminal domains of human NFU, which most likely reflect the structural characteristics expected for full-length human NFU.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / metabolism
  • Carrier Proteins / chemistry*
  • Carrier Proteins / metabolism
  • Carrier Proteins / physiology*
  • Crystallography
  • Humans
  • Iron-Sulfur Proteins / chemistry*
  • Iron-Sulfur Proteins / metabolism
  • Iron-Sulfur Proteins / physiology*
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Peptide Fragments / physiology
  • Protein Binding / physiology
  • Protein Structure, Tertiary


  • Bacterial Proteins
  • Carrier Proteins
  • Iron-Sulfur Proteins
  • NFU1 protein, human
  • Peptide Fragments
  • nifS protein, Bacteria

Associated data

  • PDB/1EG5
  • PDB/1XHJ
  • PDB/1XJH
  • PDB/2K1H