Biophysical characterization of heme binding to the intrinsically disordered region of Bach1

Kei Segawa, Miki Watanabe-Matsui, Kengo Tsuda, Toshitaka Matsui, Mikako Shirouzu, Kazuhiko Igarashi, Kazutaka Murayama

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Transcriptional repressor Bach1 plays an important role in antioxidant response. Bach1 function is regulated by heme binding to the four cysteine-proline (CP) motifs in Bach1, which leads to inhibition of its activity. Three of these CP motifs are located N-terminal to the bZip (basic leucine zipper) domain that is responsible for DNA binding. Based on sequence analysis, the region surrounding these CP motifs was expected to be intrinsically disordered. Bach1 is one of few known intrinsically disordered proteins that accept multiple heme molecules for functional regulation, but the molecular mechanisms of heme binding and functional regulation remain unclear. Uncovering these mechanisms is important for understanding Bach1-mediated antioxidant response. Biophysical characterization revealed that 5-coordinated heme binding was unique to the CP motifs within the heme-binding region of Bach1, whereas 6-coordinated binding occurred nonspecifically. Comparison of the wild-type protein and a CP motif mutant indicated that the level of 6-coordinated heme binding was reduced in the absence of 5-coordinated heme binding. Analytical ultracentrifugation showed that the CP motif mutant protein had a more elongated conformation than the wild-type protein, suggesting that cysteines within the CP motifs contribute to intramolecular interactions in Bach1. Thus, heme binding at the CP motifs induces a global conformational change in the Bach1 heme-binding region, and this conformational change, in turn, regulates the biological activity of Bach1.

Original languageEnglish
Pages (from-to)361-369
Number of pages9
JournalEuropean Biophysics Journal
Issue number4
Publication statusPublished - 2019 May 1


  • CP motif
  • Cysteine reactivity
  • Heme
  • Intrinsically disordered proteins
  • Protein conformation

ASJC Scopus subject areas

  • Biophysics


Dive into the research topics of 'Biophysical characterization of heme binding to the intrinsically disordered region of Bach1'. Together they form a unique fingerprint.

Cite this