RECOMBINANT PRO-REGIONS FROM PAPAIN AND PAPAYA PROTEINASE TV ARE SELECTIVE HIGH-AFFINITY INHIBITORS OF THE MATURE PAPAYA ENZYMES

Proteolytic enzymes require the presence of their pro-regions for corr ect folding, Of the four proteolytic enzymes from Carica papaya, papai n and papaya proteinase IV (PPIV) have 68% sequence identity. We find that their pro-regions are even more similar, exhibiting 73.6% identit y, cDNAs encoding the pro-regions of these two proteinases have been e xpressed in Escherichia coli independently from their mature enzymes, The recombinant pro-regions of papain and PPIV have been shown to be h igh affinity inhibitors of ah four of the mature native papaya cystein e proteinases, Their inhibition constants are in the range 10(-6)-10(- 9) M, PPIV was inhibited two to three orders of magnitude less effecti vely than papain, chymopapain and caricain, The pro-region of PPIV, ho wever, inhibited its own mature enzyme more effectively than did the p roregion of papain, Alignment of the sequences of the four papaya enzy mes shows that there is a highly variable section towards the C-termin al of the pro-region, This region may therefore confer selectivity to the pro-regions for the individual proteolytic enzymes.