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

Abstract

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 hemeregulated 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 Mn 2؉ /Mg 2؉ -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.

Bacteria capture iron from heme by keeping tetrapyrrol skeleton intact

“…We propose that the deferrochelation activity represents their physiological function, enabling heme iron acquisition without internalization of heme, a potentially hazardous substance in the case of EfeB orthologs and without production of CO, an antibacterial gas. Porphyrins and heme efflux pumps have been identified in several organisms (27,28). In addition, EfeB orthologs are present in many Gram-positive species.…”

The two-component system ChrSA is crucial for haem tolerance and interferes with HrrSA in haem-dependent gene regulation in Corynebacterium glutamicum

“…In fact, this function of ChrSA was expected due to the conserved microsynteny of this genomic locus where an operon of a TCS system is found in divergent orientation to hrtBA encoding a putative 'haem-regulated' ABC-transport system. This genomic organization is highly conserved among Gram-positive bacteria and homologous HrtAB transport systems were described as being required for coping with toxic haem concentrations for the species C. diphtheriae, Staphylococcus aureus and Bacillus anthracis (Bibb & Schmitt, 2010;Stauff et al, 2008). So far, this transport system has mainly been described in pathogenic species where it is of major importance during host infection, when the bacteria are exposed to high haem concentrations in the blood.…”

“…It was shown in a recent study that the haem-regulated ABC transport system, HrtAB, is crucial for C. diphtheriae to cope with elevated haem concentrations (Bibb & Schmitt, 2010). The HrtAB system consists of the permease HrtB and the ATPase HrtA and is widespread among Gram-positive bacteria (Stauff et al, 2008;Stauff & Skaar, 2009a, b). In C. diphtheriae, hrtBA expression was shown to be activated in the presence of haem by the TCS ChrSA (Bibb et al, 2005;Bibb & Schmitt, 2010).…”

Specificity of Staphylococcal Superantigen-Like Protein 10 toward the Human IgG1 Fc Domain

“…The expression of SSL10 and other SSLs appears to be tightly regulated (13), and although naturally occurring seroconversion against SSL10 has been detected in most normal individuals, only weak expression of SSL10 is observed under normal liquid culture conditions across different S. aureus strains (data not shown). Strong expression of multiple ssls, including ssl10, has been observed in a staphylococcal mutant that is defective in iron export (11).…”

“…Intriguingly, an isogenic mutant of S. aureus that is defective in an iron exporter reveals a striking increase in ssl expression when the strain is fed hemin, the organism's natural source of iron. This strain is hypervirulent in a mouse model of infection and forms numerous large liver abscesses (11)(12)(13).…”