Mutation of Schizophyllum commune metacaspases for the prevention of autoproteolysis in vitro

Metacaspases are cysteine proteases that are part of the caspase family. These enzymes are found in fungi, protozoa, and plants and have relevance in the discovery of new antifungal drugs. All metacaspases contain a nucleophilic cysteine residue in their active site that forms a dyad with a histidine residue to hydrolyze peptide bonds after arginine and lysine residues. Many metacaspases also depend on calcium for their activity and can undergo autoproteolysis, in which they are cleaved into smaller fragments. Autoproteolysis at the prodomain or linker region has been found to be crucial for the activation of metacaspases, and some metacaspases undergo further autoproteolysis upon incubation with calcium. Three types of metacaspases have been discovered. Our work focuses on the five Type I metacaspases of Schizophyllum commune, which have been previously characterized with their optimal calcium and pH conditions discovered. In order to obtain crystal structures of these metacaspases, it is essential to identify and mutate any cleavage sites in order to be able to purify full-length protein. It is also essential to understand how these cleavages affect the activity of the enzyme. Mutants have been created with mutations at the proposed cleavage sites of Metacaspase 1 without the prodomain (MC1ˆ†pro), and deletion mutants containing the individual cleavage fragments have been made to study their activities. Activity assay results show that all of these mutations result in a less active form of the enzyme when cleaving small peptides. Time course assay results confirm that mutating the proposed cleavage sites of the enzyme results in fewer fragments as analyzed by SDS-PAGE gels. Future work will be directed at applying this same work to the protein with its prodomain intact and expanding these findings to the other S. commune metacaspases.