Effects from Metal Ion in Tumor Endothelial Marker 8 and Anthrax Protective Antigen: BioLayer Interferometry Experiment and Molecular Dynamics Simulation Study

Jia Z, et al., 38(15):1183-1190, J Comput Chem, 2017

Anthrax is a bacterial infectious disease caused by Bacillus anthracis. Anthrax intoxication initiates when anthrax protective antigen (PA), a component of anthrax toxin, binds to anthrax toxin receptors such as the tumor endothelial marker 8 (TEM8) located on the cell surface. TEM8 is also known to play a key role in the angiogenic processes that can enhance tumor growth, hence making it an excellent target for tumor-specific therapies. TEM8 is a von Willebrand factor type A protein that contains a divalent cation in a metal-ion dependent adhesion site (MIDAS domain). By using a molecular dynamics simulation study, reported herein is the effects of different divalent cations on the interaction between TEM8 and PA. Also the binding affinity between TEM8 and PA in the presence of different metal ions (Mg2+ and Ca2+) was studied experimentally by using Bio-Layer Interferometry (BLI). A Pall ForteBio Octet RED instrument equipped with Anti-GST (GST) Biosensor probes was used to perform the BLI experiments. GST sensor tips were immobilized with GST-tagged TEM8 (TEM8-GST). Association and dissociation kinetics of PA were analyzed by immersing the TEM8-GST loaded sensor tips into various concentrations of PA solutions in the presence of MgCl2, CaCl2, or both. The BLI data were fitted globally. The kon, kdiss, and KD values were determined. Collectively, the results of this study suggest that the metal ions play a significant role in PA-TEM8 binding affinity, and the PA-TEM8 interaction prefers Mg2+ over Ca2+ as the divalent cation.

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