Journal Article Protein oxidation mediated by heme-induced active site conversion specific for heme-regulated transcription factor, iron response regulator

Kitatsuji, Chihiro  ,  Izumi, Kozue  ,  Nambu, Shusuke  ,  Kurogochi, Masaki  ,  Uchida, Takeshi  ,  Nishimura, Shin-Ichiro  ,  Iwai, Kazuhiro  ,  O'Brian, Mark R.  ,  Ikeda-Saito, Masao  ,  Ishimori, Koichiro

6p.18703 , 2016-01-05 , Nature Publishing Group
The Bradyrhizobium japonicum transcriptional regulator Irr (iron response regulator) is a key regulator of the iron homeostasis, which is degraded in response to heme binding via a mechanism that involves oxidative modification of the protein. Here, we show that heme-bound Irr activates O-2 to form highly reactive oxygen species (ROS) with the "active site conversion" from heme iron to non-heme iron to degrade itself. In the presence of heme and reductant, the ROS scavenging experiments show that Irr generates H2O2 from O-2 as found for other hemoproteins, but H2O2 is less effective in oxidizing the peptide, and further activation of H2O2 is suggested. Interestingly, we find a time-dependent decrease of the intensity of the Soret band and appearance of the characteristic EPR signal at g = 4.3 during the oxidation, showing the heme degradation and the successive formation of a non-heme iron site. Together with the mutational studies, we here propose a novel "two-step self-oxidative modification" mechanism, during which O-2 is activated to form H2O2 at the heme regulatory motif (HRM) site and the generated H2O2 is further converted into more reactive species such as OH at the non-heme iron site in the His-cluster region formed by the active site conversion.

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