Identification and characterization of Schizophyllum commune type I metacaspases

The role of programmed cell death in filamentous fungi is not well-understood, but is important due to the role of fungi in opportunistic infections. Plants, fungi and protozoa do not have caspase genes, but instead express the homologous proteins denoted metacaspases. To better understand the role of metacaspases in fungi we present an analysis of the sequences and activities of all five Type I metacaspases from Schizophyllum commune (ScMC), a mushroom-forming basiodmycete that undergoes sexual reproduction. The five Type I metacaspases of S. commune can be divided into two groups based on sequence similarity. Enzymes both with and without the N-terminal prodomain are active, but here we report on the constructs without the prodomains (Δpro). All five ScMCΔpro proteins show the highest enzymatic activity between pH 7 and 8 and require calcium for optimal activity. Optimal Ca(2+) concentrations for ScMC1Δpro and ScMC2Δpro are 50 mM, while ScMC3, ScMC4Δpro and ScMC5Δpro activity is optimal around 5 mM calcium. All five S. commune metacaspases have similar substrate specificity. They are most active with Arg in the P1 position and inactive with Asp in the P1 position.