Targeting sterylglucosidase 1 attenuates virulence and enables immune protection against Candida albicans

ABSTRACT Sterylglucosidases are fungus-specific enzymes that regulate ergosterol 3-β-D-glucoside (Erg-SG) homeostasis and represent promising targets for antifungal intervention. Previous studies demonstrated that sterylglucosidases from Cryptococcus neoformans and Aspergillus fumigatus contribute to fungal virulence, and that deletion of these enzymes elicits protective immunity. However, whether sterylglucosidase-mediated pathways similarly influence Candida albicans pathogenicity remains unknown. Here, we identified C. albicans Sgl1 as a bona fide sterylglucosidase that selectively hydrolyzes Erg-SG but not fungal glucosylceramide. Deletion of SGL1 resulted in marked Erg-SG accumulation without altering glucosylceramide levels, confirming its conserved role in sterylglucoside homeostasis. Although the Δ sgl 1 mutant displayed largely preserved growth, morphogenesis, and stress adaptation, it exhibited impaired biofilm formation. Biochemical characterization, inhibitor profiling, and structural analyses revealed marked species-specific inhibitor susceptibility among fungal sterylglucosidases despite highly conserved overall architecture and catalytic machinery. Structural modeling and docking studies identified differences in ligand positioning and active-site interactions that likely contribute to these divergent pharmacological responses. Functionally, loss of SGL1 significantly attenuated virulence in a murine model of systemic candidiasis. Importantly, vaccination with heat-killed Δ sgl 1 cells conferred 70% protection against lethal systemic challenge and markedly reduced kidney fungal burden, providing the first evidence that sterylglucosidase-dependent vaccination can induce protective immunity against a non-pulmonary fungal infection. Collectively, these findings establish C. albicans Sgl1 as a conserved regulator of sterylglucoside homeostasis, fungal pathogenicity, and host protection, and identify fungal sterylglucosidases as promising targets for antifungal drug and immunotherapy development. IMPORTANCE Fungal infections are associated with substantial morbidity and mortality, yet effective immunotherapies and novel antifungal targets remain limited. Candida albicans is a major cause of invasive and mucosal fungal disease, highlighting the need for new therapeutic strategies. Here, we identify the fungus-specific sterylglucosidase Sgl1 as a conserved regulator of ergosterol 3-β-D-glucoside homeostasis and a critical determinant of C. albicans pathogenicity. We further demonstrate that fungal sterylglucosidases exhibit distinct species-specific pharmacological responses despite conserved structural frameworks, revealing opportunities for rational antifungal drug design. Importantly, deletion of SGL1 attenuated virulence and enabled protective vaccination against lethal systemic candidiasis, providing the first evidence that targeting sterylglucoside metabolism can elicit protective immunity against a non-pulmonary fungal pathogen. Together, these findings identify Candida albicans Sgl1 as a promising target for antifungal drug and immunotherapy development.