Utilization of Host Iron Sources by Corynebacterium diphtheriae: Multiple Hemoglobin-Binding Proteins Are Essential for the Use of Iron from the Hemoglobin-Haptoglobin Complex

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Abstract
The use of hemin iron byCorynebacterium diphtheriaerequires the DtxR- and iron-regulated ABC hemin transporter HmuTUV and the secreted Hb-binding protein HtaA. We recently described two surface anchored proteins, ChtA and ChtC, which also bind hemin and Hb. ChtA and ChtC share structural similarities to HtaA; however, a function for ChtA and ChtC was not determined. In this study, we identified additional host iron sources that are utilized byC. diphtheriae. We show that severalC. diphtheriaestrains use the hemoglobin-haptoglobin (Hb-Hp) complex as an iron source. We report that anhtaAdeletion mutant ofC. diphtheriaestrain 1737 is unable to use the Hb-Hp complex as an iron source, and we further demonstrate that achtA-chtCdouble mutant is also unable to use Hb-Hp iron. Single-deletion mutants ofchtAorchtCuse Hb-Hp iron in a manner similar to that of the wild type. These findings suggest that both HtaA and either ChtA or ChtC are essential for the use of Hb-Hp iron. Enzyme-linked immunosorbent assay (ELISA) studies show that HtaA binds the Hb-Hp complex, and the substitution of a conserved tyrosine (Y361) for alanine in HtaA results in significantly reduced binding.C. diphtheriaewas also able to use human serum albumin (HSA) and myoglobin (Mb) but not hemopexin as iron sources. These studies identify a biological function for the ChtA and ChtC proteins and demonstrate that the use of the Hb-Hp complex as an iron source byC. diphtheriaerequires multiple iron-regulated surface components.

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