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 Staphylococcus aureus isolates. These peptides contribute to the pathogenesis of S. aureus infections, participating in multiple inflammatory responses. Here, we report a new role for S. aureus PSMs in high mobility group box-1 protein (HMGB1) induced inflammation by modulating toll-like receptor (TLR) 4 pathway. Direct ligation of TLR4 with S. aureus 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 in vitro 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 S. aureus 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 S. aureus infections.

An immunoinformatic approach driven by experimental proteomics: in silico design of a subunit candidate vaccine targeting secretory proteins of Leishmania donovani amastigotes

“…Notably, this rearrangement also involved participation of other critical histidine (His431, His555) residues at the TLR4-TLR4* interface [80] unlike the unbound structure (Additional file 8: Figure S5). Overall, these events are congruent with non-canonical TLR4 activation model mediated by microbial peptides, metals and cationic lipid nano-carriers, which are suggested to not confer canonical interaction with other monomers but to induce bond rearrangement among receptor monomers upon interaction [74][75][76][77]. Although the exact mechanism remains to be elucidated, our observations suggest that the vaccine construct may possess a characteristic peptide feature of a non-canonical TLR4 ligand [81,82], which may facilitate TLR4-TLR4* dimerization for downstream activation of immune cells.…”

“…Vaccine-specific, but not parasite protein-specific humoral response was predicted, and this can be used as a biomarker of vaccine efficacy [46,73] without eliciting a parasite-specific B cell response. Moreover, the construct structure showed a good binding affinity in previously reported binding cavity of TLR4 [74][75][76][77].…”

An immunoinformatic approach driven by experimental proteomics: in silico design of a subunit candidate vaccine targeting secretory proteins of Leishmania donovani amastigotes

“…Vaccine specific, but not parasite protein specific humoral response was predicted, and this can be used as biomarker of vaccine efficacy [38,60] without eliciting parasite specific B-cell response. Moreover, the construct structure showed good binding affinity in previously reported binding cavity of TLR4 [61][62][63][64]. The structural interface between TLR4 and the peptide adjuvant (APPHALS) used here has been extensively studied, in which the position occupied by the adjuvant peptide in the TLR4-MD2 complex has been suggested to be varying depending on its position in vaccine model and canonical activation of receptor was proposed to be mechanized by insertion of peptide adjuvant in MD2 [65].…”

Anti-inflammatory, anti-oxidative stress and novel therapeutic targets for cholestatic liver injury

“…Inflammation-induced cell damage can Neutrophil-mediated inflammatory response is the main mechanism of liver damage during cholestasis, so the study of specific signaling pathways for concentrated neutrophil aggregation during cholestasis has brought new therapeutic targets for the treatment of cholestatic liver injury. In recent years, studies have found that receptors recognize damage-associated molecular patterns (DAMPs) and thereby activate immune cells, ultimately stimulating a sterile inflammatory response (16).…”

“…Among the most important PRRs are Toll-like receptors (TLRs), which are a class of transmembrane receptors with a wide distribution. TLR4 is an important PRR that mediates signal transduction (16).…”