Primary structure of CC-III, the glycosylated cysteine proteinase from the latex of Carica candamarcensis Hook.

The amino acid sequence of the cysteine proteinase CC-III from the latex of the subtropical species Carica candamarcensis Hook has been determined with the exception of seven residues (pos. 180-186). It was deduced from the sequence analysis of the whole chain and peptides obtained by tryptic, chymotryptic, peptic and thermolysinolytic hydrolysis. CC-III consists of 214 amino acid residues. Out of a total of eight cysteine residues, six are located at positions involved in the formation of the three disulfide bridges stabilizing the structure of papain related enzymes. CC-III from Carica candamarcensis is a glycoprotein with the carbohydrate moiety bound to asparagine at position 44. Out of 210 residues compared with the sequences of the four cysteine proteinases of Carica papaya L., CC-III shares 125 identical ones (59.5%) with papain, 142 (67.6%) with papaya proteinase IV, 146 (69.5%) with papaya proteinase III and 156 (74.3%) with chymopapain. All amino acid residues constituting the active site and subsite S2 in chymopapain are conserved in CC-III with the exception of the substitution Leu157--> Val in the latter. This fact as well as the highest degree of identity between CC-III and chymopapain point to a similar specificity of both enzymes and thus CC-III might be a suitable substitute for chymopapain as a chemonucleolytic agent.