TY - JOUR
T1 - Bach1, a heme-dependent transcription factor, reveals presence of multiple heme binding sites with distinct coordination structure
AU - Hira, Shusuke
AU - Tomita, Takeshi
AU - Matsui, Toshitaka
AU - Igarashi, Kazuhiko
AU - Ikeda-Saito, Masao
N1 - Copyright:
Copyright 2009 Elsevier B.V., All rights reserved.
PY - 2007
Y1 - 2007
N2 - The mammalian transcription factor Bach1 functions as a repressor of the enhancers of heme oxygenase-1 (HO-1) gene (Hmox-1) by forming heterodimers with the small Maf proteins such as MafK. The transcription of Hmox-1 is regulated by the substrate of HO-1, heme. Heme induces expression of Hmox-1 in part by inhibiting the binding of Bach1 to the enhancers and inducing the nuclear export of Bach1. A dipeptide motif of cysteine and proline (CP motif) in Bach1 is essential for the heme-mediated regulation. In this study, we show that five molecules of heme bind to Bach1 by the heme-titration assay. The Bach1-heme complex exhibits an absorption spectrum with a major Soret peak at 371 nm and Raman band at 343 cm-1 in high amounts of heme and a spectrum containing the major Soret peak at 423 nm at low heme concentrations. The spectroscopic characterization indicates that Bach1 has two kinds of heme-binding sites with different coordination structures. Mutagenesis studies have established that four molecules of heme bind to the cysteine residues of four CP motifs in the C terminus of Bach1. These results raise the possibility that two separated activities of Bach1, DNA-binding and nuclear export, are regulated by heme binding at the different CP motifs of Bach1 respectively, but not by cooperative heme-binding.
AB - The mammalian transcription factor Bach1 functions as a repressor of the enhancers of heme oxygenase-1 (HO-1) gene (Hmox-1) by forming heterodimers with the small Maf proteins such as MafK. The transcription of Hmox-1 is regulated by the substrate of HO-1, heme. Heme induces expression of Hmox-1 in part by inhibiting the binding of Bach1 to the enhancers and inducing the nuclear export of Bach1. A dipeptide motif of cysteine and proline (CP motif) in Bach1 is essential for the heme-mediated regulation. In this study, we show that five molecules of heme bind to Bach1 by the heme-titration assay. The Bach1-heme complex exhibits an absorption spectrum with a major Soret peak at 371 nm and Raman band at 343 cm-1 in high amounts of heme and a spectrum containing the major Soret peak at 423 nm at low heme concentrations. The spectroscopic characterization indicates that Bach1 has two kinds of heme-binding sites with different coordination structures. Mutagenesis studies have established that four molecules of heme bind to the cysteine residues of four CP motifs in the C terminus of Bach1. These results raise the possibility that two separated activities of Bach1, DNA-binding and nuclear export, are regulated by heme binding at the different CP motifs of Bach1 respectively, but not by cooperative heme-binding.
KW - Heme binding mode
KW - Heme mediated regulation
KW - Heme oxygenase
KW - Spectroscopic characterization
KW - Transcription factor
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U2 - 10.1080/15216540701225941
DO - 10.1080/15216540701225941
M3 - Review article
C2 - 17701549
AN - SCOPUS:34547948422
VL - 59
SP - 542
EP - 551
JO - Biochemistry and Molecular Biology International
JF - Biochemistry and Molecular Biology International
SN - 1521-6543
IS - 8-9
ER -