Pandonodin: a proteobacterial lasso peptide with an exceptionally long C-terminal tail.

Lasso peptides are a family of ribosomally synthesized and post-translationally modified peptide (RiPP) defined by their threaded-ring topology. The N-terminus of the peptide forms an isopeptide bond with an aspartate or glutamate sidechain to create a 7- to 9-aa macrocyclic ring, through which the rest of the peptide is threaded. The result is a highly constrained 3D structure. Even though they share a threaded-ring feature, characterized lasso peptides vary greatly in sequence and size, ranging from 14 to 26 aa. Using genome mining, we identified a new lasso peptide gene cluster with a predicted lasso peptide that is 33 aa long. Here we report the heterologous expression of this new peptide, pandonodin, its NMR structure, and its unusual biophysical properties. Pandonodin has a long, proteolytically resistant 18-residue tail of low sequence complexity, which limits its water solubility. Within this tail is a 6 aa disulfide-bonded macrocycle that serves as a steric lock to maintain the lasso structure. T...