POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
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<strong>BLAST</strong> X Poster #48<br />
THE GraS/GraR TWO-COMPONENT SYSTEM AND DERMASEPTIN RESISTANCE IN<br />
STAPHYLOCOCCUS AUREUS<br />
Mélanie Falord 1 , Pierre Joanne 2 , Chahrazade El Amri 2 , and Tarek Msadek 1<br />
Biology <strong>of</strong> Gram-positive Pathogens 1 , Department <strong>of</strong> Microbiology, Institut Pasteur, 25 rue du<br />
Dr. Roux, 75015 Paris, France<br />
Peptidome de la peau des amphibiens 2 , FRE 2852, CNRS, Université Pierre et Marie Curie, 2<br />
place Jussieu, 75251 Paris 75005, France<br />
Staphylococcus aureus, a major Gram-positive human pathogen, is a leading cause <strong>of</strong><br />
both nosocomial and community infections due to its considerable capacity for adaptation.<br />
S. aureus is able to resist Cationic Anti-Microbial Peptides (CAMPs) by increasing its positive<br />
cell surface charges through D-alanylation <strong>of</strong> wall teichoic acids and lysylination <strong>of</strong><br />
phospholipids, leading to electrostatic repulsion <strong>of</strong> CAMPs. Synthesis <strong>of</strong> the major enzymes<br />
involved in these mechanisms (DltA, MprF) is positively controlled by the GraS/GraR twocomponent<br />
system. Two-component systems are bacterial signal transduction pathways with a<br />
sensor histidine kinase that is autophosphorylated in response to specific environmental stimuli<br />
and then transfers the phosphoryl group to its cognate response regulator which consequently<br />
regulates target gene expression. In S. aureus, GraS is involved in CAMP sensing, promoting<br />
bacterial resistance through GraR.<br />
Here, we have shown that a ∆graRS mutant in S. aureus is sensitive to Colistin and<br />
Dermaseptins. Moreover, we demonstrated that the graRS genes are part <strong>of</strong> a three-gene<br />
operon also containing graX, a gene with unknown function but essential to the system, and<br />
defined the operon transcriptional start site. To define the mechanism by which GraS, GraR and<br />
GraX confer CAMP resistance to S. aureus, the three proteins were overexpressed and purified<br />
to test their in vitro interactions. A potential GraR binding site upstream from the vraFG operon,<br />
known to be controlled by GraS/GraR, was identified both by in silico analysis and lacZ<br />
transcriptional fusion experiments.<br />
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