Staphylococcus aureus Phenol-Soluble Modulins α1–α3 Act as Novel Toll-Like Receptor (TLR) 4 Antagonists to Inhibit HMGB1/TLR4/NF-κB Signaling Pathway

Abstract

Phenol-soluble modulins (PSMs) have recently emerged as key virulence determinants, particularly in highly aggressive <i>Staphylococcus aureus</i> isolates. These peptides contribute to the pathogenesis of <i>S. aureus</i> infections, participating in multiple inflammatory responses. Here, we report a new role for <i>S. aureus</i> PSMs in high mobility group box-1 protein (HMGB1) induced inflammation by modulating toll-like receptor (TLR) 4 pathway. Direct ligation of TLR4 with <i>S. aureus</i> PSMα1-α3 and PSMβ1-β2 was identified by surface plasmon resonance. Remarkably, the binding affinity of TLR4 with HMGB1 was attenuated by PSMα1-α3. Further study revealed that PSMα1-α3 directly inhibited HMGB1-induced NF-κB activation and proinflammatory cytokines production <i>in vitro</i> using HEK-Blue hTLR4 cells and THP-1 cells. To analyze the molecular interactions between PSMs and TLR4, blast similarity search was performed and identified that PSMα1 and PSMβ2 were ideal templates for homology modeling. The three-dimensional structures of PSMα2, PSMα4, PSMβ1, and δ-toxin were successfully generated with MODELLER, and further refined using CHARMm. PSMs docking into TLR4 were done using ZDOCK, indicating that PSMα1-α3 compete with HMGB1 for interacting with the surrounding residues (336-477) of TLR4 domain. Our study reveals that <i>S. aureus</i> PSMα1-α3 can act as novel TLR4 antagonists, which account at least in part for the staphylococcal immune evasion. Modulation of this process will lead to new therapeutic strategies against <i>S. aureus</i> infections.