The AgrD N-Terminal Leader Peptide of Staphylococcus aureus Has Cytolytic and Amyloidogenic Properties

Abstract

Staphylococcus aureus virulence is coordinated through the Agr quorum-sensing system to produce an array of secreted molecules. One important class of secreted virulence factors is the phenol-soluble modulins (PSMs). PSMs are small-peptide toxins that have recently been characterized for their roles in infection, biofilm development, and subversion of the host immune system. In this work, we demonstrate that the signal peptide of the S. aureus quorum-sensing signal, AgrD, shares structural and functional similarities with the PSM family of toxins. The efficacy of this peptide (termed N-AgrD) beyond AgrD propeptide trafficking has never been described before. We observe that N-AgrD, like the PSMs, is found in the amyloid fibrils of S. aureus biofilms and is capable of forming and seeding amyloid fibrils in vitro. N-AgrD displays cytolytic and proinflammatory properties that are abrogated after fibril formation. These data suggest that the N-AgrD leader peptide affects S. aureus biology in a manner similar to that described previously for the PSM peptide toxins. Taken together, our findings suggest that peptide cleavage products can affect cellular function beyond their canonical roles and may represent a class of virulence factors warranting further exploration.

Staphlyococcus aureus Phenol-Soluble Modulins Stimulate the Release of Proinflammatory Cytokines from Keratinocytes and Are Required for Induction of Skin Inflammation

“…PSM peptides were synthesized by LifeTein (South Plainfield, NJ) and assayed to be Ͼ90% pure by high-performance liquid chromatography (HPLC). Synthetic peptides were prepared as previously described (33). Briefly, the peptides were resuspended in hexafluoroisopropanol (HFIP), and 0.5 mg was aliquoted into microcentrifuge tubes.…”

Recognition of Bacterial Signal Peptides by Mammalian Formyl Peptide Receptors

“…Moreover, other FPR agonists, such as phenol-soluble modulin peptide toxins (15), amyloid-␤(1-42) (8), or PAR (57), may also fit into this scheme. For example, a recent study demonstrated that the signal peptide of the Staphylococcus aureus quorum-sensing signal, AgrD, shares clear structural and functional similarities with the phenol-soluble modulin family (50). The fact that critical agonist features as described here extend to a number of distinct FPR agonists suggests that our results should prove useful in future developments, such as the identification of the FPR ligand binding site and the discovery of subtype-selective FPR antagonists.…”

“…3G), predicting that rev-W-peptide should function as a potent FPR activator. When we tested this, we found indeed nearly identical EC 50 values for this peptide on hFPR1 and mFpr1 (Fig. 3H).…”

“…Listed is a set of nine bacterial signal peptides that we initially identified, their sources, sequences, accession numbers (UniProt database), and mean EC 50 values (in nM) with respect to the activation of heterologously expressed hFPR1, mFpr1, hFPR2, mFpr2, hFPR3, and mFpr-rs1. …”

Amyloid Structures as Biofilm Matrix Scaffolds

“…Thus, PSMs are bifunctional proteins that may be stored as inert fibrils in a sessile biofilm until conditions arise that favor their dissociation to promote biofilm disassembly and virulence (47). Recent evidence suggests that PSM aggregation can be accelerated by the presence of trace amounts of AgrD, the signal peptide of the S. aureus quorum-sensing system, since AgrD would self-aggregate and act as seeds, allowing the incorporation of PSMs into the growing aggregate (53).…”