Expression, purification and characterization of the second Kunitz-type protease inhibitor domain of the human WFIKKN protein

Recently we have described a novel secreted protein (the WFIKKN protein) that consists of multiple types of protease inhibitory modules, including two tandem Kunitz-type protease inhibitor-domains. On the basis of its homologies we have suggested that the WFIKKN protein is a multivalent protease inhibitor that may control the action of different proteases. In the present work we have expressed the second Kunitz-type protease inhibitor domain of the human protein WFIKKN in Escherichia coli , purified it by affinity chromatography on trypsin-Sepharose and its structure was characterized by CD spectroscopy. The recombinant protein was found to inhibit trypsin (K (i) = 9.6 nm), but chymotrypsin, elastase, plasmin, pancreatic kallikrein, lung tryptase, plasma kallikrein, thrombin, urokinase or tissue plasminogen activator were not inhibited by the recombinant protein even at 1 mum concentration. In view of the marked trypsin-specificity of the inhibitor it is suggested that its physiological target may be trypsin.