title: The GraS Sensor in Staphylococcus aureus Mediates Resistance to Host Defense Peptides Differing in Mechanisms of Action.
abstract: Staphylococcus aureus uses the two-component regulatory system GraRS to sense and respond to host defense peptides (HDPs). However, the mechanistic impact of GraS or its extracellular sensing loop (EL) on HDP resistance is essentially unexplored. Strains with null mutations in the GraS holoprotein (ΔgraS) or its EL (ΔEL) were compared for mechanisms of resistance to HDPs of relevant immune sources: neutrophil α-defensin (human neutrophil peptide 1 [hNP-1]), cutaneous β-defensin (human β-defensin 2 [hBD-2]), or the platelet kinocidin congener RP-1. Actions studied by flow cytometry included energetics (ENR); membrane permeabilization (PRM); annexin V binding (ANX), and cell death protease activation (CDP). Assay conditions simulated bloodstream (pH 7.5) or phagolysosomal (pH 5.5) pH contexts. S. aureus strains were more susceptible to HDPs at pH 7.5 than at pH 5.5, and each HDP exerted a distinct effect signature. The impacts of ΔgraS and ΔΕL on HDP resistance were peptide and pH dependent. Both mutants exhibited defects in ANX response to hNP-1 or hBD-2 at pH 7.5, but only hNP-1 did so at pH 5.5. Both mutants exhibited hyper-PRM, -ANX, and -CDP responses to RP-1 at both pHs and hypo-ENR at pH 5.5. The actions correlated with ΔgraS or ΔΕL hypersusceptibility to hNP-1 or RP-1 (but not hBD-2) at pH 7.5 and to all study HDPs at pH 5.5. An exogenous EL mimic protected mutant strains from hNP-1 and hBD-2 but not RP-1, indicating that GraS and its EL play nonredundant roles in S. aureus survival responses to specific HDPs. These findings suggest that GraS mediates specific resistance countermeasures to HDPs in immune contexts that are highly relevant to S. aureus pathogenesis in humans.
authors.affiliation: Division of Molecular Medicine, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Division of Infectious Diseases, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA.
authors.forename: Siyang
authors.initials: S
authors.lastname: Chaili
authors.affiliation: Department of Microbiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Ambrose L
authors.initials: AL
authors.lastname: Cheung
authors.affiliation: Division of Infectious Diseases, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA The David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
authors.forename: Arnold S
authors.initials: AS
authors.lastname: Bayer
authors.affiliation: Division of Infectious Diseases, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA The David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
authors.forename: Yan Q
authors.initials: YQ
authors.lastname: Xiong
authors.affiliation: Division of Molecular Medicine, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA The David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Waring
authors.affiliation: Department of Microbiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Guido
authors.initials: G
authors.lastname: Memmi
authors.affiliation: Department of Microbiology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Niles
authors.initials: N
authors.lastname: Donegan
authors.affiliation: School of Bioresources and Bioscience, Chung-Ang University, Anseong, Republic of Korea.
authors.forename: Soo-Jin
authors.initials: SJ
authors.lastname: Yang
authors.affiliation: Division of Molecular Medicine, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Division of Infectious Diseases, Los Angeles County Harbor-UCLA Medical Center, Torrance, California, USA Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, USA The David Geffen School of Medicine at UCLA, Los Angeles, California, USA MRYeaman@ucla.edu.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Yeaman
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity
chemical_list: D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D050505:Mutant Proteins