Caulosegnins I–III: A Highly Diverse Group of Lasso Peptides Derived from a Single Biosynthetic Gene Cluster

Abstract

Lasso peptides are natural products of ribosomal origin with a unique knotted structural fold. Even though only a few of them are known, recent reports of newly isolated lasso peptides were scarce. In this work, we report the identification of a novel lasso peptide gene cluster from <i>Caulobacter segnis</i>, that produces three new lasso peptides (caulosegnins I, II, and III) using a single biosynthetic machinery. These lasso peptides possess different ring sizes and amino acid sequences. In this study, we have developed a system for enhanced lasso peptide production to allow isolation of these compounds through heterologous expression in <i>Escherichia coli</i>. We were able to elucidate the structure of the most abundant lasso peptide caulosegnin I via NMR spectroscopic analysis and performed a thorough mutational analysis that gave insight into their biosynthesis and revealed important factors affecting the stabilization of the lasso fold in general. The caulosegnins also show a diverse behavior when subjected to thermal denaturation, which is exceptional as all lasso peptides were believed to have an intrinsic high thermal stability