The present invention relates to the field of structural biology and drug discovery. More specifically, the present invention relates to novel fusion proteins, their uses and methods in three-dimensional structural analysis of macromolecules, such as X-ray crystallography and high-resolution Cryo-EM, and their use in structure-based drug design and screening, and as pharmacological tools. Even more specifically, the invention relates to a functional fusion of a toxin and a scaffold protein wherein the folded scaffold protein interrupts the topology of the toxin by insertion in an exposed β-turn of a β-strand-containing domain of said toxin to form a rigid fusion protein that retains its high affinity target binding capacity.