Characterisation of type I metacaspases of the filamentous ascomycete Podospora anserina

In the filamentous ascomycete Podospora anserina two genes were identified coding for metacaspases PaMCA1 and PaMCA2, structural homologues to mammalian caspases. Metacaspases are found in plants, fungi and protozoa and are involved in apoptosis as well as in the regulation of vital processes. Until now, only metacaspases from type I with a characteristical amino terminal pro-domain have been identified in fungi. The biological substrates of these metacaspases are widely unknown. Comparative protein analyses in P. anserina suggest a catalase-peroxidase as a putative substrate of metacaspase PaMCA1. This enzyme is important for protection against oxidative stress in the cell. Further analyses demonstrated that activity of two catalases was reduced or not detectable in PaMca1 overexpression strains compared to wild-type and deletion strains after treatment with hydrogen peroxide, an inducer of metacaspase activity. Immunodetection with an antibody against catalase-peroxidase identified increased amounts of degradation products of the corresponding protein in PaMca1 overexpression strains after hydrogen peroxide treatment. In contrast to PaMCA1 no or very low proteolytic activity of PaMCA2 could be detected. Nevertheless, compared to the wild-type, PaMca2 overexpression strains are characterised by 22% life span extension suggesting a beneficial role of this enzyme. Localisation studies with PaMCA2-GFP fusion proteins identify a condensed signal that is apparently not colocalised to the nucleus or vacuoles.