Maj. Taylor et al., RECOMBINANT PRO-REGIONS FROM PAPAIN AND PAPAYA PROTEINASE TV ARE SELECTIVE HIGH-AFFINITY INHIBITORS OF THE MATURE PAPAYA ENZYMES, Protein engineering, 8(1), 1995, pp. 59-62
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.