Isolation and purification of cysteine peptidases from the latex of Araujia hortorum fruits: Study of their esterase activities using partial least-squares (PLS) modeling

Three new cysteine peptidases (araujiain h-I, araujiain h-II and araujiain h-III) were isolated and purified to mass spectroscopy homogeneity from the latex of Araujia hortorum (Asclepiadaceae) fruits by ultracentrifugation and ion exchange chromatography. The enzymes have molecular masses of 24,030.87, 23,718 and 23,545.5 (mass spectrometry), respectively. The peptidases were activated by thiol compounds and inhibited by common thiol blocking reagents, particularly E-64 and HgCl2, suggesting that the enzymes belong to the cysteine peptidases family. A quantitative structure–activity relationship study of their esterolytic activities was performed by means of partial least-squares regression and using the novel filtering technique called orthogonal signal correction. The numerical characterization of the variation in the physicochemical features of the N-α-carbobenzoxy-aminoacid-p-nitrophenyl esters used in the PLS regression modeling was accomplished by using a large number of descriptors extracted from the literature, based on various lipophilicity, polarity and steric scales of the amino acid side-chains in combination with a set of property descriptors derived from semiempirical calculations. From the obtained results it can be concluded that all hydrophobic, electronic, and steric factors are important in the esterase activity of the cysteine peptidases studied.