Cloning of a novel cyanobacterial serotonin N-acetyltransferase gene CySNAT3 and its integration with transcriptomic drug repurposing in pediatric obstructive sleep-disordered breathing.

BACKGROUND: Melatonin has potential therapeutic value in pediatric obstructive sleep-disordered breathing (oSDB). However, plant-based melatonin extraction faces limitations including long growth cycles, low yield, and complex purification procedures. Cyanobacteria, as photosynthetic microorganisms, offer distinct advantages such as rapid growth, low cultivation cost, and well-established genetic manipulation tools, making them ideal chassis cells for producing high-value natural products. Meanwhile, the molecular mechanisms linking tonsillar pathology to oSDB severity remain poorly understood, and translational therapeutic targets are urgently needed. METHODS: A novel cyanobacterial serotonin N-acetyltransferase gene (CySNAT3) was cloned, expressed in E. coli, and purified by Ni-NTA affinity chromatography. Its enzymatic activity was assessed by HPLC-fluorescence. Separately, differential expression analysis, WGCNA, and drug repurposing were performed on tonsillar RNA-seq data (GSE274855), followed by molecular docking to validate drug-target interactions. RESULTS: CySNAT3 catalyzed the conversion of serotonin to N-acetylserotonin and 5-MT to melatonin, providing an enzymatic tool for microbial melatonin production. Four high-confidence candidate drugs (sulfamethoxazole, cimetidine, diethylstilbestrol, clofibrate) were identified, with molecular docking confirming favorable binding affinities to their target proteins (CYP2C19, SLC47A1, WNT7A, SCD). CONCLUSION: Cimetidine and diethylstilbestrol have been experimentally linked to the melatonin pathway, suggesting that these four drugs may act through modulation of melatonin signaling. This study provides a new molecular foundation for pediatric oSDB treatment by integrating a novel cyanobacterial SNAT enzyme tool with transcriptome-derived drug candidates.