<i>S</i> -nitrosylation of the CLIP-protease, Persephone, Regulates <i>Drosophila</i> innate immunity

ABSTRACT Nitric oxide (NO) modulates innate immunity, but its molecular targets in Drosophila melanogaster are largely undefined. A key mechanism of NO signalling is S -nitrosylation, the modification of cysteine thiols. The homeostasis of S -nitrosylation is maintained by S -nitrosoglutathione reductase (Gsnor), encoded by the fdh gene in D. melanogaster . As reduced Gsnor activity enhances pathogen sensitivity in plants, we investigated its role in D. melanogaster . Here, we show that flies lacking fdh exhibit increased susceptibility to the fungus Beauveria bassiana and the bacterium Staphylococcus aureus , pathogens combatted by the Toll pathway. This immune deficiency correlates with impaired Toll-dependent antimicrobial peptide expression. We demonstrate that the Toll pathway protease Persephone (Psh) is S -nitrosylated in vivo and that loss of Gsnor prevents its proteolytic activation following infection. We propose a model where Gsnor-mediated regulation of NO is essential for Toll activation, preventing excessive S -nitrosylation of Psh and ensuring a robust immune response.