Patent ID: 7767788

Claim:
A fusion protein comprising a ubiquitin insert protein having an insert regulatory domain lying between an amino terminal and a carboxyl terminal of the ubiquitin insert protein; and, a barnase target protein having a surface loop that begins at an alpha carbon of an initial terminal amino acid of the surface loop and terminates at an alpha carbon of a terminal amino acid of the surface loop, the surface loop comprising a cytotoxic target domain of the barnase target protein, wherein, the ubiquitin insert protein is inserted at a point within the surface loop between the alpha carbon of the initial amino acid of the surface loop and the alpha carbon of the terminal amino acid of the surface loop, such that an amino-carboxyl length of the ubiquitin insert protein is at least two-times greater than an alpha-carbon-alpha-carbon length of the surface loop of the barnase target protein wherein the insert regulatory domain exists in either a folded or unfolded conformation and the target cytotoxic domain exists in either a folded or unfolded conformation, the insert regulatory domain and the target cytotoxic domain comprising a cooperative and reversible conformational equilibrium such that if the insert regulatory domain is in its folded conformation, the target cytotoxic domain is in its unfolded conformation and vice versa.