Anthrax toxin is transported into human cells after its protective antigen (PA) binds to its receptor. The receptor, tumor endothelial marker 8 (TEM8), has been identified as a potential anticancer target for its involvement in angiogenesis. This project investigates the role of the metal ion in the TEM8/PA binding mechanism to provide information relevant to anticancer therapy development. Structures of the TEM8/PA complex were produced through homology modeling, and canonical conformational ensembles of the TEM8/PA complexes involving different metal ions in TEM8 were generated through molecular dynamics simulations. Binding thermodynamics were also assessed using a Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) method. In addition, the dissociation constant between TEM8 and PA in the presence of different divalent metal ions was determined experimentally via fluorescence resonance energy transfer (FRET). Both computational and experimental results indicate the metal ion in TEM8 contributes significantly to the binding affinity. Simulation shows the existence of Mg2+, Zn2+ or Ca2+ in TEM8 corresponds to a sequentially reduced affinity between TEM8 and PA. Further, computational analyses suggest the differences in TEM8/PA affinity are consistent with the behavior of closely related integrin proteins known to adopt two conformations (open and closed) correlated with different levels of activity.
Jia, Zhe; Ackroyd, Christine; Christensen, Kenneth; and Dominy, Brian, "An investigation into the effect of metal ion in PA and TEM8 binding" (2015). Graduate Research and Discovery Symposium (GRADS). 186.