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.