The human antimicrobial peptide LL-37 binds directly to CsrS, a sensor histidine kinase of group A Streptococcus, to activate expression of virulence factors.
Group A Streptococcus (GAS) responds to subinhibitory concentrations of LL-37 by up-regulation of virulence factors through the CsrRS (CovRS) two-component system. The signaling mechanism, however, is unclear. To determine whether LL-37 signaling reflects specific binding to CsrS or rather a nonspecific response to LL-37-mediated membrane damage, we tested LL-37 fragments for CsrRS signaling and for GAS antimicrobial activity. We identified a 10-residue fragment (RI-10) of LL-37 as the minimal peptide that retains the ability to signal increased expression of GAS virulence factors, yet it has no detectable antimicrobial activity against GAS. Substitution of individual key amino acids in RI-10 reduced or abrogated signaling. These data do not support the hypothesis that CsrS detects LL-37-induced damage to the bacterial cell membrane but rather suggest that LL-37 signaling is mediated by a direct interaction with CsrS. To test whether LL-37 binds to CsrS, we used the purified CsrS extracellular domain to pull down LL-37 in vitro, a result that provides further evidence that LL-37 binds to CsrS. The dissociation of CsrS-mediated signaling from membrane damage by LL-37 fragments together with in vitro evidence for a direct LL-37-CsrS binding interaction constitute compelling evidence that signal transduction by LL-37 through CsrS reflects a direct ligand/receptor interaction.
From the Division of Infectious Diseases, Boston Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115.
Jorge J
JJ
Velarde
From the Division of Infectious Diseases, Boston Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115.
Melissa
M
Ashbaugh
From the Division of Infectious Diseases, Boston Children's Hospital and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts 02115 Michael.Wessels@childrens.harvard.edu.
Michael R
MR
Wessels
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins / Q000378:metabolism*; D054804:Cathelicidins / Q000494:pharmacology / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D013297:Streptococcus pyogenes / Q000201:enzymology / Q000235:genetics*; D015533:Transcriptional Activation; D015854:Up-Regulation; D037521:Virulence Factors / Q000096:biosynthesis / Q000235:genetics*
D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D001426:Bacterial Proteins; D054804:Cathelicidins; D037521:Virulence Factors; D011494:Protein Kinases; C432144:CsrS protein, bacteria
Antimicrobial Peptide (AMP); Cell Surface Receptor; Histidine Kinase; Host-Pathogen Interaction; Streptococcus pyogenes (S. pyogenes)