Abstract:
:Heme oxygenases convert heme to free iron, CO, and biliverdin. Saccharomyces cerevisiae and Candida albicans express putative heme oxygenases that are required for the acquisition of iron from heme, a critical process for fungal survival and virulence. The putative heme oxygenases Hmx1 and CaHmx1 from S. cerevisiae and C. albicans, respectively, minus the sequences coding for C-terminal membrane-binding domains, have been expressed in Escherichia coli. The C-terminal His-tagged, truncated enzymes are obtained as soluble, active proteins. Purified ferric Hmx1 and CaHmx1 have Soret absorption maxima at 404 and 410 nm, respectively. The apparent heme binding Kd values for Hmx1 and CaHmx1 are 0.34 +/- 0.09 microM and 1.0 +/- 0.2 microM, respectively. The resonance Raman spectra of Hmx1 reveal a heme binding pocket similar to those of the mammalian and bacterial heme oxygenases. Several reductants, including ascorbate, yeast cytochrome P450 reductase (CPR), human CPR, spinach ferredoxin/ferredoxin reductase, and putidaredoxin/putidaredoxin reductase, are able to provide electrons for biliverdin production by Hmx1 and CaHmx1. Of these, ascorbate is the most effective reducing partner. Heme oxidation by Hmx1 and CaHmx1 regiospecifically produces biliverdin IXalpha. Spectroscopic analysis of aerobic reactions with H2O2 identifies verdoheme as a reaction intermediate. Hmx1 and CaHmx1 are the first fungal heme oxygenases to be heterologously overexpressed and characterized. Their heme degradation activity is consistent with a role in iron acquisition.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Kim D,Yukl ET,Moënne-Loccoz P,Montellano PRdoi
10.1021/bi061429rsubject
Has Abstractpub_date
2006-12-12 00:00:00pages
14772-80issue
49eissn
0006-2960issn
1520-4995journal_volume
45pub_type
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