Cysteine Peptidases of Calotropis procera (Apocynaceae): A Literature Review on their Biochemical Properties and Potential Applications

Abstract: The latex of the xerophytic plant Calotropis procera, popularly known as giant milkweed, contains a complex mixture of secondary metabolites and proteins and has attracted the attention of many researchers. Several bioactive laticifer enzymes from C. procera have been studied for their potential applications in the medical, agricultural and food industries. The present work aimed to review the current scientific knowledge on cysteine peptidases from the latex of this plant, highlighting their biochemical properties and possible uses as biotechnological tools. Bibliographic databases (PubMed, Scopus and Web of Science) were searched for scientific works published in the last six decades reporting the purification, biochemical characterization, molecular cloning and potential applications of laticifer cysteine peptidases from C. procera. Since the first works published in the late 1960s on the occurrence of thiol peptidases in this species, five cysteine peptidases (procerain, procerain B, CpCP-1, CpCP-2 and CpCP-3) have been purified and biochemically characterized. The characterized enzymes are members of the subfamily C1A of sulfhydryl proteases, showing the characteristic biochemical and structural features of papain and related proteins. Several biological activities of the purified enzymes have been demonstrated, including the inhibition of phytopathogenic fungi and milk coagulation properties, which may be of practical use. Moreover, pharmacologically active propeptides released from the posttranslational processing of C. procera cysteine peptidase zymogens have been shown to be promising therapeutic agents against cancer cells. Further research is needed to provide a better comprehensive understanding of the mode of action and biosafety of these molecules.