Ancestral Sequence Reconstruction Provides Insights into the Structural Diversification and Neofunctionalization of T-superfamily Conotoxins in Conus.

Due to their remarkable diversity and rapid evolution, conotoxins-peptide toxins from predatory marine cone snails-provide a powerful system for exploring how gene diversification may contribute to the development of lineage-specific adaptations. We previously demonstrated that 2-loop Tau conotoxins represent an evolutionary innovation associated with mollusk-hunting behaviors in cone snails. Here, we investigate the evolutionary history of these toxins as a model to understand the mechanism of ancestral gene neofunctionalization, which may have contributed to the emergence of mollusk-hunting in cone snails. Using ancestral sequence reconstruction, we present a model in which ancestral T-superfamily conotoxins neofunctionalized into the 2-loop Tau conotoxins. Predicted ancestral sequences reveal an intermediate structure between the classic T-superfamily conotoxins and the derived 2-loop Tau forms. Notably, these ancestral intermediates acquired a new cysteine scaffold that facilitated a structural transition from a globular to a ribbon fold. This conformational shift was followed by sequence-level changes that presumably enhanced activity against molecular targets in mollusks. We propose that the emergence of 2-loop Tau conotoxins may have been one factor that contributed to the emergence of molluscivory, providing insight into how gene innovation may underlie ecological diversification.