Unified free energy landscapes of non-disulfide-bonded μ conotoxins differ in population depending on folding pathway

Conotoxins are short, disulfide-rich peptide toxins produced by aquatic snails. Due to their strong selectivity for receptors involved in neuromuscular transmission, they are promising therapeutic leads. Because the number of disulfide connectivities grows rapidly with the number of cysteines, it can be difficult to ascertain the native folded structure or whether there even is a native fold rather than an ensemble of "disulfide isomers." The μ conotoxins contain six cysteines and exist in a folding spectrum. In this article, we employ the composite diffusion map approach to study their unified folding landscape with unconnected disulfides. We identify important nonlinear collective modes and demonstrate that hirudin-like folders occupy a region associated with hydrophobic collapse, while BPTI-like folders occupy a region associated with extended states. This work sheds important light on the free energy landscapes of μ-conotoxins and quantifies the sequence contribution to these landscapes.