Patent ID: 8211428

Claim:
A method for identifying or selecting a protease or catalytically active portion thereof that cleaves a cleavage sequence in a protein target substrate, comprising: a) contacting a collection comprising a plurality of different mutant proteases and/or catalytically active portions thereof that comprise the mutations(s) with a protease trap polypeptide, wherein: the protease trap polypeptide is a serpin or modified serpin, an alpha macroglobulin or a modified member of the alpha macroglobulin family, or, a p35 protein or a modified member of the p35 family; the protease trap polypeptide comprises a reactive site containing a cleavage sequence for the protein target substrate, or is modified in its reactive site by replacement of one or more of amino acids in the P4-P2′ positions of the protease trap polypeptide to include the cleavage sequence of the protein target substrate; contacting is effected under conditions for cleavage of amino acids in the cleavage sequence in the protease trap polypeptide by a protease or a catalytically active portion thereof in the collection to form stable complexes containing the protease trap polypeptide covalently linked to a protease or catalytically active portion thereof; upon cleavage of amino acids in the cleavage sequence in the protease trap polypeptide by a protease or catalytically active portion thereof in the collection, the protease trap polypeptide forms a a stable complex with a protease or catalytically active portion thereof in the collection; b) separating the complexed proteases from uncomplexed members of the collection; and c) identifying or selecting the protease or catalytically active portion thereof in the complex, thereby identifying or selecting a protease or catalytically active portion thereof that cleaves the protein target substrate.