Heme-iron utilization by Leptospira interrogans requires a heme oxygenase and a plastidic-type ferredoxin-NADP+ reductase

• Leptospira interrogans heme oxygenase (LepHO) was purified and characterized.
• The redox partner of LepHO was found to be a ferredoxin-NADP+ reductase (FNR).
• L. interrogans FNR and LepHO accomplish heme degradation to iron and biliverdin.
• Heme cleavage by LepHO does not require a ferredoxin.
• A novel substrate of a plastidic-type FNR was identified.

BackgroundHeme oxygenase catalyzes the conversion of heme to iron, carbon monoxide and biliverdin employing oxygen and reducing equivalents. This enzyme is essential for heme-iron utilization and contributes to virulence in Leptospira interrogans.MethodsA phylogenetic analysis was performed using heme oxygenases sequences from different organisms including saprophytic and pathogenic Leptospira species. L. interrogans heme oxygenase (LepHO) was cloned, overexpressed and purified. The structural and enzymatic properties of LepHO were analyzed by UV–vis spectrophotometry and 1H NMR. Heme-degrading activity, ferrous iron release and biliverdin production were studied with different redox partners.ResultsA plastidic type, high efficiently ferredoxin-NADP+ reductase (LepFNR) provides the electrons for heme turnover by heme oxygenase in L. interrogans. This catalytic reaction does not require a ferredoxin. Moreover, LepFNR drives the heme degradation to completeness producing free iron and α-biliverdin as the final products. The phylogenetic divergence between heme oxygenases from saprophytic and pathogenic species supports the functional role of this enzyme in L. interrogans pathogenesis.ConclusionsHeme-iron scavenging by LepHO in L. interrogans requires only LepFNR as redox partner. Thus, we report a new substrate of ferredoxin-NADP+ reductases different to ferredoxin and flavodoxin, the only recognized protein substrates of this flavoenzyme to date. The results presented here uncover a fundamental step of heme degradation in L. interrogans.General significanceOur findings contribute to understand the heme-iron utilization pathway in Leptospira. Since iron is required for pathogen survival and infectivity, heme degradation pathway may be relevant for therapeutic applications.