STRUCTURAL REQUIREMENTS FOR CATHEPSIN-B AND CATHEPSIN-H INHIBITION BYKININOGENS

Domain 3 (D3) of human kininogens, the major cysteine proteinase inhib itors in plasma, has been shown to be the tightest binding inhibitory domain for cathepsins B and H. D3 was expressed in three fragments as its exon products as follows: exon 7 (Gly235-Gln292), exon 8 (Gln292-G ly328), and exon 9 (Gln329-Met357). Exon products 7, 8, and 9 alone as well as exon product 7 + 9 each exhibited an IC50 value 5- to 30-fold higher (5-30 mu M) than exon products 7 + 8 and 8 + 9 (0.9-1.3 mu M) for cathepsins B and H, respectively. However, in turn, the exon produ cts 7 + 8 and 8 + 9 seemed to be less potent inhibitors than the intac t D3 (10, 200 nM) or HK (200, 500 nM) molecule. These results clearly indicate that an intact molecule of HK or its domain 3 as a whole is r equired for optimal inhibition of cathepsins B and H.