A Centipede Toxin Family Defines an Ancient Class of CSαβ Defensins.

Summary Disulfide-rich peptides (DRPs) play diverse physiological roles and have emerged as attractive sources of pharmacological tools and drug leads. Here we describe the 3D structure of a centipede venom peptide, U-SLPTX 15 -Sm2a, whose family defines a unique class of one of the most widespread DRP folds known, the cystine-stabilized α/β fold (CSαβ). This class, which we have named the two-disulfide CSαβ fold (2ds-CSαβ), contains only two internal disulfide bonds as opposed to at least three in all other confirmed CSαβ peptides, and constitutes one of the major neurotoxic peptide families in centipede venoms. We show the 2ds-CSαβ is widely distributed outside centipedes and is likely an ancient fold predating the split between prokaryotes and eukaryotes. Our results provide insights into the ancient evolutionary history of a widespread DRP fold and highlight the usefulness of 3D structures as evolutionary tools. Graphical Abstract Highlights • A centipede toxin structure defines a distinct type of the CSαβ defensin fold • This fold is characterized by two disulfides versus at least three in other CSαβ peptides • 2ds-CSαβ peptides are widespread in both eukaryotes and prokaryotes • The 2ds-CSαβ fold probably has an ancient pre-eukaryotic origin Disulfide-rich peptides (DRPs) play many important physiological roles, and can be extremely taxonomically widespread. Here, Dash et al. show that a diverse centipede toxin family belongs to one of the most widespread DRP folds known, the cysteine-stabilized α/β fold, but that it represents a unique, ancient form of this fold. [ABSTRACT FROM AUTHOR]