Scalable Biosynthetic Production of Knotted Peptides Enables ADME and Thermodynamic Folding Studies

Knotted peptides present a wealth of structurally diverse, biologically active molecules, with the inhibitor cystine knot/knottin class among the most ecologically common ones. Many of these natural products interact with extracellular targets such as voltage-gated ion channels with exquisite selectivity and potency, making them intriguing therapeutic modalities. Such compounds are often produced in low concentrations by intractable organisms, making structural and biological characterization challenging, which is frequently overcome by various expression strategies. Here, we sought to test a biosynthetic route for the expression and study of knotted peptides. We screened expression constructs for a biosynthesized knotted peptide to determine the most influential parameters for successful disulfide folding and used NMR spectroscopic fingerprinting to validate topological structures. We performed pharmacokinetic characterization, which indicated that the interlocking disulfide structure minimizes liabilities of linear peptide sequences, and propose a mechanism by which knotted peptides are cleared. We then developed an assay to monitor solution folding in real time, providing a strategy for studying the folding process during maturation, which provided direct evidence for the importance of backbone organization as the driving force for topology formation.