Structural and functional modulation of human kynurenine aminotransferase I enhances selenium-driven redox metabolism for cancer therapy.

Se-methylselenocysteine (MSC) is a redox-active selenium-containing amino acid with notable anticancer potential, requiring enzymatic activation for cytotoxicity. Human kynurenine aminotransferase 1 (hKYAT1) catalyzes MSC through transamination and β-elimination pathways, generating β-methylselenopyruvate and methylselenol, both of which induce oxidative stress and epigenetic modulation. To enhance MSC metabolism and its therapeutic efficacy, we performed site-directed mutagenesis targeting three critical hKYAT1 residues: Tyr101, Asp126, and Phe278. These mutants, along with wild-type hKYAT1, were expressed in hepatocellular carcinoma cell lines HepG2 and Huh7, and their impact on enzymatic activity, cytotoxic effects, apoptosis and chromatin remodeling were evaluated. Several mutations significantly enhanced MSC metabolism, with Y101H and F278A increasing both transamination and β-elimination activity, and D126L favoring β-elimination. These modifications led to a five-to 30-fold increase in MSC-induced cytotoxicity compared to wild-type hKYAT1. Additionally, mutant hKYAT1 expression altered histone deacetylase (HDAC) profiles, increased histone H4 acetylation, and activated apoptotic signaling through caspase cleavage and cytochrome c release. Collectively, our findings demonstrate that rational engineering of hKYAT1 can potentiate MSC metabolism and amplify its anticancer effects, offering a promising enzyme-targeting strategy for selenium-based cancer therapies.