Structural and biochemical analyses of a lasso peptide natural product containing an unusual disulfide bond between consecutive cysteines.

Lasso peptides are a group of ribosomally synthesized and post-translationally modified peptides with a unique lariat topology. They have been classified into four classes based on disulfide bond patterns. In this study, we isolated a lasso peptide containing a disulfide bond in the macrocyclic ring, which is identical to jiangxilassin A. Analysis of the three-dimensional solution structure of this peptide suggested that the disulfide bond enhances the rigidity of the macrocyclic ring. To investigate whether the disulfide bond is required for enzymatic modification, we replaced either cysteine residue with serine. Upon heterologous expression, both mutants produced disulfide-linked dimers that retained macrolactam ring formation, dehydration, and methylation, although their production levels were substantially lower than the level observed for the wild type. These results indicate that the vicinal disulfide bond is not strictly required for these post-translational modifications but contributes to the efficient production of jiangxilassin A.