Melleatin, an antibiofilm multitasking protein with rRNA N-glycosylase and nuclease activity from Armillaria mellea fruiting bodies

Several studies highlight the identification of some enzymes with additional abilities, especially those involved in metabolic pathways and/or host defence processes, classified as multitasking proteins. In this context, we report the characterization of melleatin (17.5-kDa), a multitasking enzyme isolated from Armillaria mellea fruiting bodies. Melleatin inhibits protein synthesis and displayed unexpected enzymatic action. Indeed, the structural characterization (primary structure and 3D model) showed that melleatin belongs to the His-Me finger endonucleases superfamily possessing a fold like the biofilm-dispersing nuclease NucB, the latter isolated from the marine Bacillus licheniformis. The enzymatic studies on melleatin showed that this enzyme is able to: i) inhibit protein synthesis in a rabbit reticulocyte lysate system (IC₅₀ value 16.48 ± 3.71 nM); ii) damage rabbit and Trichoderma harzianum ribosomes as a ribosome inactivating protein (β-fragment release after Endo's assay); and iii) hydrolyse DNA. Functionally, melleatin has antibiofilm action and antifungal activity towards T. harzianum and Botrytis cinerea affecting fungal ribosomes, while it does not exhibit cytotoxicity against different human cell lines, being unable to enter the cells. Overall, melleatin represents a novel multitasking protein that could be used as a biotechnological tool for its antibiofilm and antifungal activity or as a toxic component of biomedical bioconstructs.