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Subsite differences between the active centres of papaya peptidase A and papain as revealed by affinity chromatography. Purification of papaya peptidase A by ionic-strength-dependent affinity adsorption on an immobilized peptide inhibitor of papain.

ABSTRACT: An affinity column consisting of the specific peptide inhibitor of papain, Gly-Gly (O-benzyl)Tyr-Arg, attached to Sepharose was found to bind the active thiol proteinase papaya peptidase A specifically, but only at an ionic strength significantly higher than the one at which papain is bound. When a mixture of active papaya peptidase A and its irreversibly oxidized contaminant was applied to the column, the active enzyme was bound whereas the inactive material was not. The bound enzyme was released by deionized water and found to contain 1 mol of SH group/mol of protein. The different conditions required for the binding of the two enzymes to the immobilized peptide was shown to reflect different ionic-strength-dependences of the affinity of the two enzymes for the peptide in solution. Whereas the affinity of papain for the inhibitor appears to be insensitive to ionic strength over the range studied, that of papaya peptidase A is ionic-strength-dependent and always lower than that of papain. A rate assay is devised for papaya peptidase A with N-benzyloxycarbonylglycine p-nitrophenyl ester as the substrate at pH 5.5. After calibration against an active-site titration the assay yields the thiol-group concentration without interference from inactive contaminants. For the papaya peptidase A-catalysed hydrolysis of N-benzyloxycarbonylglycine p-nitrophenyl ester at pH 5.5 kcat. was found to be 16.7s-1, which is about 3 times the value found for the same reaction catalysed by papain.

SUBMITTER: Schack P

PROVIDER: S-EPMC1153538 | biostudies-other | 1984 May

REPOSITORIES: biostudies-other

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Project description:BackgroundPapain-like cysteine proteases (PLCPs), a large group of cysteine proteases structurally related to papain, play important roles in plant development, senescence, and defense responses. Papain, the first cysteine protease whose structure was determined by X-ray crystallography, plays a crucial role in protecting papaya from herbivorous insects. Except the four major PLCPs purified and characterized in papaya latex, the rest of the PLCPs in papaya genome are largely unknown.ResultsWe identified 33 PLCP genes in papaya genome. Phylogenetic analysis clearly separated plant PLCP genes into nine subfamilies. PLCP genes are not equally distributed among the nine subfamilies and the number of PLCPs in each subfamily does not increase or decrease proportionally among the seven selected plant species. Papaya showed clear lineage-specific gene expansion in the subfamily III. Interestingly, all four major PLCPs purified from papaya latex, including papain, chymopapain, glycyl endopeptidase and caricain, were grouped into the lineage-specific expansion branch in the subfamily III. Mapping PLCP genes on chromosomes of five plant species revealed that lineage-specific expansions of PLCP genes were mostly derived from tandem duplications. We estimated divergence time of papaya PLCP genes of subfamily III. The major duplication events leading to lineage-specific expansion of papaya PLCP genes in subfamily III were estimated at 48 MYA, 34 MYA, and 16 MYA. The gene expression patterns of the papaya PLCP genes in different tissues were assessed by transcriptome sequencing and qRT-PCR. Most of the papaya PLCP genes of subfamily III expressed at high levels in leaf and green fruit tissues.ConclusionsTandem duplications played the dominant role in affecting copy number of PLCPs in plants. Significant variations in size of the PLCP subfamilies among species may reflect genetic adaptation of plant species to different environments. The lineage-specific expansion of papaya PLCPs of subfamily III might have been promoted by the continuous reciprocal selective effects of herbivore attack and plant defense.

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Subsite differences between the active centres of papaya peptidase A and papain as revealed by affinity chromatography. Purification of papaya peptidase A by ionic-strength-dependent affinity adsorption on an immobilized peptide inhibitor of papain.

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