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Staphylococcus aureus HrtA Is an ATPase Required for Protection against Heme Toxicity and Prevention of a Transcriptional Heme Stress Response ^,

Department of Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee 37232,¹ Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198²

Received 10 December 2007/ Accepted 25 February 2008

During systemic infection, Staphylococcus aureus acquires nutrient iron from heme, the cofactor of vertebrate myoglobin and hemoglobin. Upon exposure to heme, S. aureus up-regulates the expression of the heme-regulated transporter, HrtAB. Strains lacking hrtAB exhibit increased sensitivity to heme toxicity, and upon heme exposure they elaborate a secreted protein response that interferes with the recruitment of neutrophils to the site of infection. Taken together, these results have led to the suggestion that hrtAB encodes an efflux system responsible for relieving the toxic effects of accumulated heme. Here we extend these observations by demonstrating that HrtA is the ATPase component of the HrtAB transport system. We show that HrtA is an Mn²⁺/Mg²⁺-dependent ATPase that functions at an optimal pH of 7.5 and exhibits in vitro temperature dependence uncommon to ABC transporter ATPases. Furthermore, we identify conserved residues within HrtA that are required for in vitro ATPase activity and are essential for the functionality of HrtA in vivo. Finally, we show that heme induces an alteration in the gene expression pattern of S. aureus hrtA, implying the presence of a novel transcriptional regulatory mechanism responsible for the previously described immunomodulatory characteristics of hrtA mutants exposed to heme.

Published ahead of print on 7 March 2008.

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