Book of Abstracts: Albany 2005
Analysis of Complexes Formed Between Anthrax Protective Antigen Monomers and Between Anthrax Protective Antigen and Models for the Human Anthrax Toxin Receptor
Bacillus anthracis, a spore-forming infectious bacterium, produces a toxin consisting of three proteins: lethal factor (LF), edema factor (EF), and protective antigen (PA) (1, 2). LF and EF possess intracellular enzymatic functions, the net effect of which is to severely compromise host innate immunity. PA exhibits a four domain structure and has a molecular weight of 83 kDa. During an anthrax infection PA plays the critical role of facilitating entry of both EF and LF toxins into host cell cytoplasm. This endocytotic event is initiated following the interaction of whole PA monomers with anthrax toxin receptors present on the host cell membrane, of which two types have been identified, TEM8 and CMG2 (3). Following the cleavage of a major portion of the amino terminal domain 1 (∼ 20 kDa) of PA with the human protein furin, a heptameric ?cup-like pre-pore? arrangement of receptor-bound truncated PA monomers (Mr ∼ 63,000) is formed, which serves as an endocytotic transport vessel for EF and/or LF (4).
Here we report the results of computational studies on wild-type vs. mutant complexes formed between receptor-bound, truncated PA monomers, and between PA monomers and models for the human, membrane associated, anthrax toxin receptor. The computational work employed a variety of approaches, including molecular dynamics simulations and ZDOCK (5) protein:protein docking simulations, as well as MolProbity (6) and GRASP2 (7) analyses on final complexes. The results confirmed the utility of the ZDOCK docking algorithm to successfully predict the wild-type complex structure for receptor-bound truncated PA monomers in the PA ?pre-pore? (as found in 1tzn.pdb) (see figure on left below), as well as the wild-type structure of PA complexed to CMGP-2, a model anthrax toxin receptor (as found in 1t6b.pdb). Mutations made in the PA loop regions, 312-315 and 512-515 (see figure on right below), were shown to adversely affect PA monomer-monomer interaction.
Gustaf H. Carlson School of Chemistry and Biochemistry
This study was supported by a research grant to D. J. N. from the National Institutes of Health (R15 AI054577-01).
References and Footnotes