The iron chaperone poly(rC)-binding protein 2 forms a metabolon with the heme oxygenase 1/cytochrome P450 reductase complex for heme catabolism and iron transfer

J Biol Chem. 2017 Aug 11;292(32):13205-13229. doi: 10.1074/jbc.M117.776021. Epub 2017 Jun 27.


Mammals incorporate a major proportion of absorbed iron as heme, which is catabolized by the heme oxygenase 1 (HO1)-NADPH-cytochrome P450 reductase (CPR) complex into biliverdin, carbon monoxide, and ferrous iron. Moreover, intestinal iron is incorporated as ferrous iron, which is transported via the iron importer, divalent metal transporter 1 (DMT1). Recently, we demonstrated that the iron chaperone poly(rC)-binding protein 2 (PCBP2) can directly receive ferrous iron from DMT1 or transfer iron to the iron exporter, ferroportin 1. To promote intracellular iron flux, an iron chaperone may be essential for receiving iron generated by heme catabolism, but this hypothesis is untested so far. Herein, we demonstrate that HO1 binds to PCBP2, but not to other PCBP family members, namely PCBP1, PCBP3, or PCBP4. Interestingly, HO1 formed a complex with either CPR or PCBP2, and it was demonstrated that PCBP2 competes with CPR for HO1 binding. Using PCBP2-deletion mutants, we demonstrated that the PCBP2 K homology 3 domain is important for the HO1/PCBP2 interaction. In heme-loaded cells, heme prompted HO1-CPR complex formation and decreased the HO1/PCBP2 interaction. Furthermore, in vitro reconstitution experiments with purified recombinant proteins indicated that HO1 could bind to PCBP2 in the presence of heme, whereas loading of PCBP2 with ferrous iron caused PCBP2 to lose its affinity for HO1. These results indicate that ferrous iron released from heme can be bound by PCBP2 and suggest a model for an integrated heme catabolism and iron transport metabolon.

Keywords: PCBP2; heme; heme oxygenase; iron; iron chaperone; iron metabolism; protein/protein interaction.

Publication types

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

MeSH terms

  • Amino Acid Substitution
  • Binding Sites
  • Binding, Competitive
  • Biological Transport
  • Cell Line
  • Gene Deletion
  • Heme / metabolism*
  • Heme Oxygenase (Decyclizing) / chemistry
  • Heme Oxygenase (Decyclizing) / genetics
  • Heme Oxygenase (Decyclizing) / metabolism
  • Heme Oxygenase-1 / antagonists & inhibitors
  • Heme Oxygenase-1 / chemistry
  • Heme Oxygenase-1 / genetics
  • Heme Oxygenase-1 / metabolism*
  • Humans
  • Iron / metabolism*
  • Metalloporphyrins / metabolism
  • Mutation
  • NADPH-Ferrihemoprotein Reductase / antagonists & inhibitors
  • NADPH-Ferrihemoprotein Reductase / chemistry
  • NADPH-Ferrihemoprotein Reductase / genetics
  • NADPH-Ferrihemoprotein Reductase / metabolism*
  • Protein Interaction Domains and Motifs
  • Protein Multimerization
  • Protein Transport
  • RNA Interference
  • RNA-Binding Proteins / chemistry
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Structural Homology, Protein
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • DMRT1 protein
  • Metalloporphyrins
  • PCBP2 protein, human
  • RNA-Binding Proteins
  • Recombinant Fusion Proteins
  • Transcription Factors
  • tin mesoporphyrin
  • Heme
  • Iron
  • HMOX1 protein, human
  • Heme Oxygenase (Decyclizing)
  • Heme Oxygenase-1
  • heme oxygenase-2
  • NADPH-Ferrihemoprotein Reductase