Alternate Ion Signalling and Its Effect on Metacaspase Activity

Metacaspase are cysteine-dependent proteases that are found in fungi, plants, and protozoa. They play a critical role in programmed cell death and innate immune response in these organisms.  Metacaspases typically cleave specifically after arginine or lysine residues when fulfilling their role in cell death or the immune response, and their activity is regulated by auto proteolysis and calcium signaling. Given the importance of metacaspases in key cellular processes, we want to understand more about how this protease is regulated by cations. S. commune metacaspases are shown to be calcium dependent, and examining how other ions interact to increase or possibly inhibit metacaspase activity can elucidate more information about how calcium and other ions bind to the protease, and what cellular factors, like alternate ion concentrations, could impact its activity. We are also hoping to explain how certain properties like the ionic radius could affect the activity of the metacaspases. This can be tested by first identifying cations chemically similar to calcium ions, and comparing the effects on activity each ion has in isolation compared to calcium using an assay that measures fluorescence based on cleavage activity. Preliminary assays show that most alternate ions lead to minimal cleavage, as seen with magnesium and manganese, or no cleavage compared to calcium dependent activity. Cations can also be tested by monitoring the sizes of proteins cleaved by the metacaspase by running SDS-PAGE gels. When the proteins are cleaved the gels show smaller fragments then when the proteins remain intact. Preliminary results show that copper, nickel and zinc are able to block calcium-induced cleavage.