Group behavior in many bacteria relies on chemically induced communication called quorum sensing (QS), which plays important roles in the regulation of colonization, biofilm formation, and virulence. In Gram-positive bacteria, QS is often mediated by cyclic ribosomally synthesized and posttranslationally modified peptides (RiPPs). Staphylococci secrete autoinducing peptides (AIPs) as signalling molecules to regulate population wide behavior. Therefore, AIPs have received attention as potential anti-virulence agents to inhibit QS in human pathogens. To investigate AIPs, we developed an effective protocol for solid-phase synthesis of peptide thiolactones by concomitant ring closure and cleavage from the solid support. The strategy was applied for mapping the importance of the structural features in the recently isolated S. schleiferi AIP by performing alanine scan and truncation studies. Furthermore, a limited number of AIP structures from non-aureus staphylococci had been identified as the minute amounts secreted in complex media renders it difficult. Thus, we developed a method for the identification of AIPs by exploiting their thiolactone functionality for chemoselective trapping and enrichment of the compounds from bacterial supernatant. Standard LC-MS analysis, guided by genome sequencing data, then readily provided the AIP identities. By using this approach, we rapidly doubled the number of identified AIPs and we expect that the method should be extendable to AIP-expressing Gram-positive bacteria beyond the staphylococcal genus. However, when attempting to identify the AIP of Listeria monocytogenes, we did not succeed. This observation ultimately led us to suggest that pentameric AIPs from Lactiplantibacillus plantarum, Clostridium perfringens, and Listeria monocytogenes, which were previously presumed to be thiolactone-containing structures, doreadily rearrange to become homodetic cyclopeptides. This finding has implications for the developing understanding of cross-species and potential cross-genus communication of bacteria and may help guide the discovery of peptide ligands to perturb their function.

Rearrangement of thiodepsipeptides by S → N Acyl shift delivers homodetic autoinducing peptides

ACS Spring 2022

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