ABSTRACTThe accessory growth regulator (Agr)-like quorum sensing (QS) system ofClostridium perfringenscontrols the production of many toxins, including beta toxin (CPB). We previously showed (J. E. Vidal, M. Ma, J. Saputo, J. Garcia, F. A. Uzal, and B. A. McClane, Mol Microbiol 83:179–194, 2012,http://dx.doi.org/10.1111/j.1365-2958.2011.07925.x) that an 8-amino-acid, AgrD-derived peptide named 8-R upregulates CPB production by this QS system. The current study synthesized a series of small signaling peptides corresponding to sequences within theC. perfringensAgrD polypeptide to investigate theC. perfringensautoinducing peptide (AIP) structure-function relationship. When both linear and cyclic ring forms of these peptides were added toagrBnull mutants of type B strain CN1795 or type C strain CN3685, the 5-amino-acid peptides, whether in a linear or ring (thiolactone or lactone) form, induced better signaling (more CPB production) than peptide 8-R for bothC. perfringensstrains. The 5-mer thiolactone ring peptide induced faster signaling than the 5-mer linear peptide. Strain-related variations in sensing these peptides were detected, with CN3685 sensing the synthetic peptides more strongly than CN1795. Consistent with those synthetic peptide results, Transwell coculture experiments showed that CN3685 exquisitely senses native AIP signals from other isolates (types A, B, C, and D), while CN1795 barely senses even its own AIP. Finally, aC. perfringensAgrD sequence-based peptide with a 6-amino-acid thiolactone ring interfered with CPB production by severalC. perfringensstrains, suggesting potential therapeutic applications. These results indicate that AIP signaling sensitivity and responsiveness vary amongC. perfringensstrains and suggestC. perfringensprefers a 5-mer AIP to initiate Agr signaling.IMPORTANCEClostridium perfringenspossesses an Agr-like quorum sensing (QS) system that regulates virulence, sporulation, and toxin production. The current study used synthetic peptides to identify the structure-function relationship for the signaling peptide that activates this QS system. We found that a 5-mer peptide induces optimal signaling. Unlike other Agr systems, a linear version of this peptide (in addition to thiolactone and lactone versions) could induce signaling. TwoC. perfringensstrains were found to vary in sensitivity to these peptides. We also found that a 6-mer peptide can inhibit toxin production by some strains, suggesting therapeutic applications.
Structure—Function Relationship of Amino Acid—[2]Rotaxanes.
