Non-native states of cardosin A induced by acetonitrile: Activity modulation via polypeptide chains rearrangements

Cardosin A (EC: 3.4.23) is an enzyme containing two polypeptide chains, purified from pistils of Cynara cardunculus L., a cardoon, used for milk clotting in cheese making. It is a member of the aspartic proteinases (APs), like pepsin and HIV-proteinase that are composed by two symmetric units comprising the active site. Cardosin A is thought to be involved in many cellular events such as in pollen–pistil interaction and adhesion dependent recognition mechanisms. In the present study, the structural and activity effects of different amounts of acetonitrile (ACN) in cardosin A are presented. The results indicate that low ACN concentrations (up to 10% ACN) reversibly stimulate the enzyme activity accompanied by slight secondary structure induction. In light of the structural and stability studies performed so far, cardosin A can adopt conformational alterations that can result in activity modulation via polypeptide chains rearrangements.