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Oxidative stress promotes degradation of the Irr protein to regulate haem biosynthesis in Bradyrhizobium japonicum
Author(s) -
Yang Jianhua,
Panek Heather R.,
O'Brian Mark R.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05087.x
Subject(s) - biology , biochemistry , dehydratase , mutant , catalase , bradyrhizobium japonicum , reactive oxygen species , heme , oxidative stress , biosynthesis , peroxidase , enzyme , rhizobiaceae , gene , bacteria , genetics , symbiosis
Summary The haem proteins catalase and peroxidase are stress response proteins that detoxify reactive oxygen species. In the bacterium Bradyrhizobium japonicum , expression of the gene encoding the haem biosynthesis enzyme δ‐aminolevulinic acid dehydratase (ALAD) is normally repressed by the Irr protein in iron‐limited cells. Irr degrades in the presence of iron, which requires haem binding to the protein. Here, we found that ALAD levels were elevated in iron‐limited cells of a catalase‐deficient mutant, which corresponded with aberrantly low levels of Irr. Irr was undetectable in wild‐type cells within 90 min after exposure to exogenous H 2 O 2 , but not in a haem‐deficient mutant strain. In addition, Irr did not degrade in response to iron in the absence of O 2 . The findings indicate that reactive oxygen species promote Irr turnover mediated by haem, and are involved in iron‐dependent degradation. We demonstrated Irr oxidation in vitro , which required haem, O 2 and a reductant. A truncated Irr mutant unable to bind ferrous haem does not degrade in vivo , and was not oxidized in vitro . We suggest that Irr oxidation is a signal for its degradation, and that cells sense and respond to oxidative stress through Irr to regulate haem biosynthesis.