Development of recombinant inhibitors specific to human kallikrein 2 using phage‐display selected substrates

The reactive site loop of serpins undoubtedly defines in part their ability to inhibit a particular enzyme. Exchanges in the reactive loop of serpins might reassign the targets and modify the serpin–protease interaction kinetics. Based on this concept, we have developed a procedure to change the specificity of known serpins. First, reactive loops are very good substrates for the target enzymes. Therefore, we have used the phage‐display technology to select from a pentapeptide phage library the best substrates for the human prostate kallikrein hK2 [Cloutier, S.M., Chagas, J.R., Mach, J.P., Gygi, C.M., Leisinger, H.J. & Deperthes, D. (2002) Eur. J. Biochem . 269 , 2747–2754]. Selected substrates were then transplanted into the reactive site loop of α1‐antichymotrypsin to generate new variants of this serpin, able to inhibit the serine protease. Thus, we have developed some highly specific α1‐antichymotrypsin variants toward human kallikrein 2 which also show high reactivity. These inhibitors might be useful to help elucidate the importance of hK2 in prostate cancer progression.