POSTERS - BLAST X - University of Utah

BLAST X Poster #48
THE GraS/GraR TWO-COMPONENT SYSTEM AND DERMASEPTIN RESISTANCE IN
STAPHYLOCOCCUS AUREUS
Mélanie Falord 1 , Pierre Joanne 2 , Chahrazade El Amri 2 , and Tarek Msadek 1
Biology of Gram-positive Pathogens 1 , Department of Microbiology, Institut Pasteur, 25 rue du
Dr. Roux, 75015 Paris, France
Peptidome de la peau des amphibiens 2 , FRE 2852, CNRS, Université Pierre et Marie Curie, 2
place Jussieu, 75251 Paris 75005, France
Staphylococcus aureus, a major Gram-positive human pathogen, is a leading cause of
both nosocomial and community infections due to its considerable capacity for adaptation.
S. aureus is able to resist Cationic Anti-Microbial Peptides (CAMPs) by increasing its positive
cell surface charges through D-alanylation of wall teichoic acids and lysylination of
phospholipids, leading to electrostatic repulsion of CAMPs. Synthesis of the major enzymes
involved in these mechanisms (DltA, MprF) is positively controlled by the GraS/GraR twocomponent
system. Two-component systems are bacterial signal transduction pathways with a
sensor histidine kinase that is autophosphorylated in response to specific environmental stimuli
and then transfers the phosphoryl group to its cognate response regulator which consequently
regulates target gene expression. In S. aureus, GraS is involved in CAMP sensing, promoting
bacterial resistance through GraR.
Here, we have shown that a ∆graRS mutant in S. aureus is sensitive to Colistin and
Dermaseptins. Moreover, we demonstrated that the graRS genes are part of a three-gene
operon also containing graX, a gene with unknown function but essential to the system, and
defined the operon transcriptional start site. To define the mechanism by which GraS, GraR and
GraX confer CAMP resistance to S. aureus, the three proteins were overexpressed and purified
to test their in vitro interactions. A potential GraR binding site upstream from the vraFG operon,
known to be controlled by GraS/GraR, was identified both by in silico analysis and lacZ
transcriptional fusion experiments.
99