Purification, crystallization and preliminary X-ray analysis of mexicain

Characterization of the proteolytic system present in Vasconcellea quercifolia latex

Vasconcellea quercifolia (Caricaceae) latex contains several cysteine endopeptidases with high proteolytic activity. Cysteine endopeptidases are the main active compounds used by the plant as a defense mechanism. A proteolytic preparation from V. quercifolia ("oak leaved papaya") latex was purified by cation exchange chromatography. From SDS-PAGE and blotting of the selected fractions, the N-terminal amino acid sequences of polypeptides were determined by Edman's degradation. The analysis by peptide mass fingerprinting (PMF) of the enzymes allowed their characterization and confirmed the presence of seven different cysteine proteinases in the latex of V. quercifolia. Moreover, the comparison between the tryptic maps with those deposited in databases using the MASCOT tool showed that none of the isolated proteases matched with another plant protease. Notably, a propeptidase was detected in the plant latex, which is being the first report in this sense. Furthermore, the cDNA of one of the cysteine proteases that is expressed in the latex of V. quercifolia was cloned and sequenced. The consensus sequence was aligned using the ClustalX web server, which allowed detecting a high degree of identity with cysteine proteases of the Caricaceae family and establishing the evolutionary relationship between them. We also observed a high conservation degree for those amino acid residues which are essential for the catalytic activity and tridimensional structure of the plant proteases belonging to the subfamily C1A. The PMF analysis strongly suggests that the sequence obtained corresponds to the VQ-III peptidase.

Purification and characterization of a cysteine endopeptidase from Vasconcellea quercifolia A. St.-Hil. latex displaying high substrate specificity

A new proteolytic preparation from Vasconcellea quercifolia ("oak leaved papaya") latex containing several cysteine endopeptidases with high proteolytic activity has been obtained. The specific activity of the new enzymatic preparation (VQ) was higher than that of Carica papaya latex. VQ was able to coagulate milk and to hydrolyze caseins and then could be used to produce cheeses and/or casein hydrolysates. Ion exchange chromatography of VQ allowed the isolation of a new protease, named quercifoliain I, homogeneous when analyzed by SDS-PAGE, IEF and MALDI-TOF-MS. Molecular mass was 24195 Da, and its isoelectric point was >9.3. The N-terminal sequence was determined (YPESVDWRQ). Insulin B-chain cleavage showed higher specificity than that of papain and was restricted to glycyl and alanyl residues at P1' position. The tryptic peptide mass fingerprint of quercifoliain I analyzed with the MASCOT search tool did not find a match with papain or any other plant cysteine proteases.