Predictive and fluorescent nanosensing experimental methods for evaluating anthrax protective antigen and lethal factor interactions for therapeutic applications.

Recently, specific interaction of anthrax protective antigen domain 4 (PAD4) and lethal factor domain 1 (LFD1) have been considered for the design of novel diagnostic and therapeutic systems in medicine. In this study, theoretical and experimental approaches were used to monitor the interactions of PAD4 and LFD1. CLusPro server and Dimplot software were used to predict the interaction of these domains. Results, revealed interactive sites between PAD4 and LFD1 on loop regions of both C and N terminal of PAD4. In experimental methods, PAD4 and LFD1 were expressed in Escherichia coli and purified for usage in Magnetic Bead (MB) and Multi-Walled Carbon Nanotubes (MWCNTs) based bio-sensing platforms. In the magnetic-based system, the magnetic sedimentation of QD-PAD4 by MBs-LFD1 and the observation of the fluorescence spectrum related to QD-PAD4 in the precipitated materials confirmed the interaction of PAD4 with LFD1 protein. In the MWCNTs-based method, the QD-PAD4 fluorescence was quenched by absorption on MWCNTs. Upon the addition of LFD1, fluorescence emission was recovered, indicating interaction of LFD1 with QD-PAD4, which results the separation of QD-PAD4 from MWCNTs surfaces and fluorescence restoration. Finally, new approaches showed the interaction of PAD4 and LFD1, which can be used as an attractive model in medicine.