The present invention provides a protein having an A chain of a ricin-like toxin, a B chain of a ricin-like toxin and a heterologous linker amino acid sequence, linking the A and B chains. The linker sequence contains a cleavage recognition site for a disease specific protease such as a cancer, inflammatory, fungal, viral or parasitic protease. The invention also relates to a nucleic acid molecule encoding the protein and to expression vectors incorporating the nucleic acid molecule. In addition, the invention relates to a method for producing the recombinant protein in yeast, to nucleic acid molecules for use in yeast and to yeast transformed with such nucleic acid molecules. Also provided is a method of inhibiting or destroying mammalian cancer cells, inflammatory cells, cells infected with a virus, a fugus, or parasite, or parasites utilizing the nucleic acid molecules and proteins of the invention and pharmaceutical compositions for treating human cancer, inflammatory disease, viral infection, fugal infection, or parasitic infection.