Interaction of cysteine proteinases with recombinant kininogen domain 2, expressed in Escherichia coli

The calpain-binding domain 2 of the kininogens, the major plasma inhibitors of cysteine proteinases, was expressed in Escherichia coli. Expression of soluble protein was optimal at 15°C and was augmented by growing the bacteria in sorbitol and betaine. The recombinant domain showed high affinity ( K i 0.3–1 nM) for cathepsin L and papain, and a somewhat lower affinity ( K i ∼ 15 nM) for calpain. The binding to cathepsin H was substantially weaker, and no inhibition of actinidin and cathepsin B was detected. The affinity for cathepsin L was comparable to that reported for the domain isolated from plasma L-kininogen, whereas the affinities for papain and calpain were about tenfold lower. The latter difference may be due to the recombinant domain being nonglycosylated.