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ABSTRACT: Staphylococcus aureus is a human pathogen responsible for most wound and hospital-acquired infections. The protein MgrA is both an important virulence determinant during infection and a regulator of antibiotic resistance in S. aureus. The crystal structure of the MgrA homodimer, solved at 2.86 A, indicates the presence of a unique cysteine residue located at the interface of the protein dimer. We discovered that this cysteine residue can be oxidized by various reactive oxygen species, such as hydrogen peroxide and organic hydroperoxide. Cysteine oxidation leads to dissociation of MgrA from DNA and initiation of signaling pathways that turn on antibiotic resistance in S. aureus. The oxidation-sensing mechanism is typically used by bacteria to counter challenges of reactive oxygen and nitrogen species. Our study reveals that in S. aureus, MgrA adopts a similar mechanism but uses it to globally regulate different defensive pathways.
Nature Chemical Biology 12/2006; 2(11):591-5. · 14.69 Impact Factor
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ABSTRACT: Toll-like receptors and other immune-signaling pathways play important roles as sensors of bacterial pattern molecules, such as peptidoglycan, lipoprotein, or teichoic acid, triggering innate host immune responses that prevent infection. Immune recognition of multiple bacterial products has been viewed as a safeguard against stealth infections; however, this hypothesis has never been tested for Staphylococcus aureus, a frequent human pathogen. By generating mutations that block the diacylglycerol modification of lipoprotein precursors, we show here that S. aureus variants lacking lipoproteins escape immune recognition and cause lethal infections with disseminated abscess formation, failing to elicit an adequate host response. Thus, lipoproteins appear to play distinct, nonredundant roles in pathogen recognition and host innate defense mechanisms against S. aureus infections.
Proceedings of the National Academy of Sciences 10/2006; 103(37):13831-6. · 9.68 Impact Factor
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ABSTRACT: Mycobacterium tuberculosis secretes ESAT-6, a virulence factor that triggers cell-mediated immune responses and IFN-gamma production during tuberculosis. ESAT-6 is transported across the bacterial envelope by a specialized secretion system with a FSD (FtsK-SpoIIIE domain) membrane protein. Although the presence of ESAT-6-like genes has been identified in the genomes of other microbes, the possibility that they may encode general virulence functions has hitherto not been addressed. Herein we show that the human pathogen Staphylococcus aureus secretes EsxA and EsxB, ESAT-6-like proteins, across the bacterial envelope. Staphylococcal esxA and esxB are clustered with six other genes and some of these are required for synthesis or secretion of EsxA and EsxB. Mutants that failed to secrete EsxA and EsxB displayed defects in the pathogenesis of S. aureus murine abscesses, suggesting that this specialized secretion system may be a general strategy of human bacterial pathogenesis.
Proceedings of the National Academy of Sciences 02/2005; 102(4):1169-74. · 9.68 Impact Factor
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ABSTRACT: Bacterial dipeptide ABC transporters function to import a wide range of dipeptide substrates. This ability to transport a wide variety of dipeptides is conferred by the cognate substrate binding protein (SBP) of these transporters. SBPs bind dipeptides with little regard for their amino acid content. Here, we report the 1.7 A resolution structure of lipoprotein-9 (SA0422) of Staphylococcus aureus in complex with the dipeptide glycylmethionine. Experimental characterization of the subcellular location of the protein confirmed that SA0422 is an acylated, peripheral membrane protein. This is the first structure determined for an SBP of a Gram-positive dipeptide ABC transporter. Usually, binding of dipeptides occurs in a binding pocket that is largely hydrated and able to accommodate the side chains of several different amino acid residues. Unlike any other known SBP, lipoprotein-9 binds the side chains of the glycylmethionine dipeptide through very specific interactions. Lipoprotein-9 shares significant structural and sequence homology with the MetQ family of methionine SBP. Sequence comparisons between MetQ-like proteins and lipoprotein-9 suggest that the residues forming the tight interactions with the methionine side chains of the ligand are highly conserved between lipoprotein-9 and MetQ homologues, while the residues involved in coordinating the glycine residue are not. Modeling of the Vibrio cholerae MetQ and lipoprotein-9 binding pockets can account for lipoprotein-9 substrate specificity toward glycylmethionine. For this reason, we have designated lipoprotein-9 GmpC, for glycylmethionine binding protein.
Biochemistry 01/2005; 43(51):16193-202. · 3.42 Impact Factor
