Metabolic modulation of TCA cycle by S-nitrosylation in Monascus spp

Monascus spp. produces several beneficial secondary metabolites (SMs), such as Monacolin K and Monascus pigments, which have wide applications in the pharmaceutical and food industries. Various factors, including gene expression, regulate the metabolic processes of Monascus spp. Furthermore, S-nitrosylation also modulates the activity of its metabolic enzymes. However, the specific regulatory role and mechanisms of S-nitrosylation in the metabolic pathways of Monascus spp. remain unexplored. In this study, quantitative S-nitrosoproteomics of M. purpureus identified 352 modified proteins, representing 12% of the total protein content in M. purpureus HJ11. S-nitrosylated proteins were predominantly distributed in glycolysis, tricarboxylic acid (TCA) cycle, amino acid metabolism and fatty acid metabolism. Notably, 87% of enzymes in the TCA cycle were S-nitrosylated. Further correlation analyses and in vitro enzymatic experiments suggest that protein S-nitrosylation inhibits the TCA cycle, thereby reducing the production of Monacolin K and Monascus pigments. To our knowledge, these findings demonstrate for the first time that S-nitrosylation serves as a key metabolic regulator in Monascus spp. This study elucidated how nitrogen-source-modulated protein S-nitrosylation inhibits the TCA cycle in Monascus spp., exerting differential effects on cell growth and the metabolic profile, including the biosynthesis of SMs, amino acids, and other key products. Our study also provides novel insights into enhancing high-value-added metabolite production in Monascus spp.