Innovative Ricin Toxin Detection: Unraveling Apurinic/Apyrimidinic Lyase Activity and Developing Fluorescence Sensors

Ricin toxin (RT) is a potential bioterrorism agent because of its high potency, extremely small lethal dose, ease of preparation, and notable stability. Therefore, a portable method is urgently required to efficiently detect and determine the presence of toxicity of RT and evaluate its potency for public health monitoring and counter-bioterrorism responses. Currently, enzyme-based assays for detecting RT mainly focus on its <i>N</i>-glycosidase activity. In this study, we demonstrated that RT exhibits apurinic/apyrimidinic (AP) lyase activity using several methods. Characterization of the enzyme reaction and kinetics revealed that AP lyase activity is optimal at 59 °C and pH 4.0. This activity is highly pH-sensitive, remaining active between pH 3.0 and pH 4.6. Furthermore, we developed a portable fluorescence-based lateral flow assay (FLFA) that detects RT much faster than existing assays based on its <i>N</i>-glycosidase activity. Moreover, this assay can efficiently detect RT at nanogram levels from complex matrix samples within 1.5 h while simultaneously determining its biological activity. In conclusion, the discovery of the AP lyase activity of RT and the development of FLFA represent novel approaches for studying the enzymatic profiles of other ribosome-inactivating proteins.