Bacillus anthracis IsdG, a Heme-Degrading Monooxygenase

ABSTRACT Bacillus anthracis, the causative agent of anthrax, utilizes hemin and hemoglobin for growth in culture, suggesting that these host molecules serve as sources for the nutrient iron during bacterial infection. Bioinformatic analyses of the B. anthracis genome revealed genes with similarity to the iron-regulated surface determinant (isd) system responsible for heme uptake in Staphylococcus aureus. We show that the protein product of one of these genes, isdG, binds hemin in a manner resembling the heme binding of known heme oxygenases. Formation of IsdG:hemin complexes in the presence of a suitable electron donor, e.g., ascorbate or cytochrome P450 reductase, promotes catalytic degradation of hemin to biliverdin with concomitant release of iron. IsdG is required for B. anthracis utilization of hemin as a sole iron source, and it is also necessary for bacterial protection against heme-mediated toxicity. These data suggest that IsdG functions as a heme-degrading monooxygenase in B. anthracis.

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Fatty Liver and Impaired Hepatic Metabolism Alters the Congener-Specific Distribution of Polychlorinated Biphenyls (PCBs) in Mice with a Liver-Specific Deletion of Cytochrome P450 Reductase

10.26434/chemrxiv.12026904.v1 ◽

2020 ◽

Author(s):

Xueshu Li ◽

Chun-Yun Zhang ◽

Hans-Joachim Lehmler

Keyword(s):

Cytochrome P450 ◽

Polychlorinated Biphenyls ◽

Fatty Liver ◽

Partition Coefficients ◽

Hepatic Metabolism ◽

Gas Chromatography Mass Spectrometry ◽

Cytochrome P450 Reductase ◽

P450 Reductase ◽

Specific Distribution ◽

Specific Deletion

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are linked to adverse health outcomes. PCB tissue levels are determinants of PCB toxicity; however, it is unclear how factors, such as an altered metabolism and/or a fatty liver, affect PCB distribution in vivo. We determined the congener-specific disposition of PCBs in mice with a liver specific deletion of cytochrome P450 reductase (KO), a model of fatty liver with impaired hepatic metabolism, and wildtype (WT) mice. Male and female KO and WT mice were exposed orally to Aroclor 1254, a technical PCB mixture. PCBs were quantified in adipose, blood, brain and liver tissues by gas chromatography-mass spectrometry. PCB profiles and levels in tissues were genotype and sex dependent. PCB levels were higher in the liver from KO compared to WT mice. PCB profiles showed clear differences between tissues from the same exposure group. While experimental tissue : blood partition coefficients in KO and WT mice did not follow the trends predicted using a composition-based model, the agreement between experimental and calculated partition coefficients was still reasonable. Thus, a fatty liver and/or an impaired hepatic metabolism alter the distribution of PCBs in mice and the magnitude of the partitioning of PCBs from blood into tissues can be approximated using composition-based models.<br>

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