PRORENIN PROCESSING AND RESTRICTED ENDOPROTEOLYSIS BY MOUSE-TISSUE KALLIKREIN FAMILY ENZYMES (MK1, MK9, MK13, AND MK22)

Four members of the tissue kallikrein family, mK1, mK9, mK13, and mK22 , all of which exhibit extensive homology in amino acid sequence among themselves, were obtained from the submandibular gland of ICR mice an d examined for their ability to cleave prorenin. Tissue kallikrein mK1 3 was confirmed to be a prorenin-converting enzyme; and mK9, which was earlier shown to be an EGF-binding protein, was found to cleave mouse Ren 2 prorenin specifically and convert it to mature renin with an ac tivity of approximately 1/10 of that of mK13. With the same substrate, mK22 (beta-NGF endopeptidase) gave two products, renin and arginyl-re nin; whereas mK1 (true tissue kallikrein) did not process it at all. T he endoproteolytic activity of tissue kallikreins was examined with va rious peptide-MCA substrates. The substrates contained three key struc tures: X(Y)-Arg-Arg, X(Y)-Lys-Arg and X-Lys-Lys motifs (where X and Y are hydrophilic and hydrophobic amino acids, respectively). We found t hat mK1, mK9 and mK13 preferentially cleaved the former two types of s ubstrate, except Y-Arg-Arg-MCA. The substrate X-Lys-Lys-MCA was hardly cleaved by these three tissue kallikreins but was preferentially clea ved by mK22. The four tissue kallikreins seem to have the ability to p rocess precursor proteins containing a pair of basic amino acid residu es; the specificities of three of the enzymes (mK1, mK9 and mK13) were similar to each other but were different from that of mK22. (C) 1998 Elsevier Science B.V.