Isolation and primary structure of the CCI papain-like cysteine proteinases from the latex of Carica candamarcensis Hook

The dried latex of the mountain papaya, Carica candamarcensis, was chromatographed on CM-Sephadex C50, giving rise to three peaks (CCI, CCII and CCIII) with amidase activity on N-α-benzoyl-DL-arginine-4-nitroanilide. The less basic, most active, peak, CCI, was separated into two components, CCIa and CCIb, by reverse-phase HPLC under denaturing conditions. The primary structures of CCla and CCIb are presented. They were deduced from sequence analysis of the whole proteins and peptides resulting from enzymatic digestions. Both proteinases are made of 213 amino acid residues, CCIb sharing 88–89% similarity with the three subvariants (G90/R212, E90/R212, E90/K212) of CCIa. 139–140 amino acid residues (65.8%) of CCIa and 141 residues (66.5%) of CCIb are common to papain. The seven cysteine residues are aligned with those of papain and the catalytic triad (Cys25, His159, Asn175) of all cysteine peptidases of the papain family is conserved. The similarity with the other cysteine proteases from Carica papaya is discussed.