Enterolyin S, a Polythiazole‐containing Hemolytic Peptide from Enterococcus caccae

The β‐hemolytic factor streptolysin S (SLS) is an important linear azol(in)e‐containing peptide (LAP) that contributes significantly to the virulence of Streptococcus pyogenes. Despite its discovery 85 years ago, SLS has evaded structural characterizing owing to its notoriously problematic physicochemical properties. Here, we report the discovery and characterization of a structurally analogous hemolytic peptide from Enterococcus caccae, termed enterolysin S (ELS). Through heterologous expression, site‐directed mutagenesis, chemoselective modification, and high‐resolution mass spectrometry, we found that ELS contains an intriguing contiguous octathiazole moiety. The discovery of ELS expands our knowledge of hemolytic LAPs by adding a new member to this virulence‐promoting family of modified peptides. The Streptolysin S (SLS)‐type of linear azol(in)e‐containing peptides (LAPs) belong to a family of ribosomally synthesized and post‐translationally modified peptides (RiPPs) known for their hemolytic activities. The chemical structure of SLS has remained elusive despite its discovery 85 years ago. We identified a novel SLS‐type hemolytic LAP named Enterolysin S and characterized its unique post‐translational modification as an unprecedented octathiazole.