Trypsin display on the surface of bacteriophage

The gene III and VIII-encoded coat proteins (pIII and pVIII) from bacteriophage M13 have been fused to the C terminus of the serine protease, trypsin (Tsn). The genes encoding the fusions were then inserted directly into M13mp18 to create vectors which expressed both the Tsn-coat protein hybrids and the wild-type (wt) coat proteins. Immunoblot analysis confirmed that the bacteriophage express Tsn on their surface. Isolated fusion phage possess kinetic parameters which approximate those of the wt enzyme. An endogenous Escherichia coli protease inhibitor, ecotin, copurifies with the Tsn phage. Immobilized ecotin can be used to selectively bind bacteriophage which express Tsn::pIII fusion proteins.