A Malassezia pseudoprotease dominates the secreted hydrolase landscape and is a potential allergen on skin.

Malassezia globosa is abundant and prevalent on sebaceous areas of the human skin. Genome annotation reveals that M. globosa possesses a repertoire of secreted hydrolytic enzymes relevant for lipid and protein metabolism. However, the functional significance of these enzymes is uncertain and presence of these genes in the genome does not always translate to expression at the cutaneous surface. In this study we utilized targeted RNA sequencing from samples isolated directly from the skin to quantify gene expression of M. globosa secreted proteases, lipases, phospholipases and sphingomyelinases. Our findings indicate that the expression of these enzymes is dynamically regulated by the environment in which the fungus resides, as different growth phases of the planktonic culture of M. globosa show distinct expression levels. Furthermore, we observed significant differences in the expression of these enzymes in culture compared to healthy sebaceous skin sites. By examining the in situ gene expression of M. globosa's secreted hydrolases, we identified a predicted aspartyl protease, MGL_3331, which is highly expressed on both healthy and disease-affected dermatological sites. However, molecular modeling and biochemical studies revealed that this protein has a non-canonical active site motif and lacks measurable proteolytic activity. This pseudoprotease MGL_3331 elicits a heightened IgE-reactivity in blood plasma isolated from patients with atopic dermatitis compared to healthy individuals and invokes a pro-inflammatory response in peripheral blood mononuclear cells. Overall, our study highlights the importance of studying fungal proteins expressed in physiologically relevant environments and underscores the notion that secreted inactive enzymes may have important functions in influencing host immunity.

Pre-existing adaptive immunity to the RNA-editing enzyme Cas13d in humans.

RNA-guided RNA-targeting nucleases, such as CRISPR-Cas13 proteins, have therapeutic potential for gene editing. Among Cas13d enzymes, Cas13d from the bacteria Ruminococcus flavefaciens (RfxCas13d) is of particular interest owing to its small size and high specificity. However, the existence of pre-existing immunity against RfxCas13d is unclear. In this study, we evaluated antibody and T cell responses to RfxCas13d in healthy donors using ELISA and T cell culture assays. We found RfxCas13d-reactive antibodies and CD4 and CD8 T cell responses in most donors, comparable to responses against Cas9 proteins from Staphylococcus aureus (SaCas9) and Streptococcus pyogenes (SpCas9). RfxCas13d-responding T cells could produce the inflammatory cytokines IFN-γ, TNF-α and IL-17. These findings should be taken into consideration in the development of RfxCas13d for therapy.