Exploring the mechanisms of action of human secretory RN ase 3 and RN ase 7 against Candida albicans

Human antimicrobial RN ases, which belong to the vertebrate RN ase A superfamily and are secreted upon infection, display a wide spectrum of antipathogen activities. In this work, we examined the antifungal activity of the eosinophil RN ase 3 and the skin‐derived RN ase 7, two proteins expressed by innate cell types that are directly involved in the host defense against fungal infection. Candida albicans has been selected as a suitable working model for testing RN ase activities toward a eukaryotic pathogen. We explored the distinct levels of action of both RN ases on yeast by combining cell viability and membrane model assays together with protein labeling and confocal microscopy. Site‐directed mutagenesis was applied to ablate either the protein active site or the key anchoring region for cell binding. This is the first integrated study that highlights the RN ases’ dual mechanism of action. Along with an overall membrane‐destabilization process, the RN ases could internalize and target cellular RNA . The data support the contribution of the enzymatic activity for the antipathogen action of both antimicrobial proteins, which can be envisaged as suitable templates for the development of novel antifungal drugs. We suggest that both human RN ases work as multitasking antimicrobial proteins that provide a first line immune barrier.