Molecular assembly of lethal factor enzyme and pre-pore heptameric protective antigen in early stage of translocation

  • Laleh AlisaraieEmail author
  • Isabelle Rouiller
Original Paper


During intoxication, the anthrax toxin lethal (LF) and edema (EF) factors initially assemble with the protective antigen (PA) on the plasma membrane of cells expressing the membrane-bound surface-exposed anthrax toxin receptor (ATR). This takes place at the physiological pH prior to entering the acidic environment of the endosome. We elucidated the molecular dynamics (MD) behaviors of the three-dimensional structure of the (PA63)7LF3 complex in various conformations and analyzed the dynamical properties of the fully loaded pre-pore complex on the plasma membrane at the physiological pH. The analysis points to the interaction networks of amino acids conserved between PA63 octamer and heptamer, which are not affected during the initial stage of the LFs binding. The simulations show an asymmetrical movement of the complex domains that directly affect LFs conformations. The conformational and structural alterations of the 2β2-2β3 loops of PA subunits are associated with pore formation. The early conformational changes of the loops appear as they peel off from the domain 2 toward domain 4 of each PA subunit. The LFs unfold in 1α1 segments of their N-terminal initiating the early stage of the pre-pore formation. The results indicate instable regions within the complex and provide important clues concerning the detail of fluctuating residues of the LF-PA interface regions at the early steps of toxins translocation.


Anthrax toxin Complexation stoichiometry Domains motilities LF unfolding Lumen asynchronous alterations 



The authors thank Compute Canada for providing free access to High Performance Computer Clusters. LA thanks Memorial University for the startup grant. IR is grateful to the Canadian Foundation for Innovation (CFI 12824 to IR), the Canadian Institutes for Health Research (CIHR) for the operating grant (MOP 86693) and the new Investigator award.

Supplementary material

894_2015_2878_Fig10_ESM.gif (11 kb)
Figure S1

Energy funnel resulted from protein-protein docking, representing the abundance of conformations. (GIF 11 kb)

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High resolution image (TIFF 8062 kb)
894_2015_2878_Fig11_ESM.gif (16 kb)
Figure S2

Alteration of PA63 during 100 ns of MD simulations. RMSD change of A. Complex (PA63)7LF3, B. Variation of Solvent Accessible Surface (GIF 15 kb)

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High resolution image (TIFF 6563 kb)
894_2015_2878_Fig12_ESM.gif (155 kb)
Figure S3

Variation of B-factor in three LF ligands. The lighter color represents the segments with higher B-factor value. The light green segments at domain 4 undergo the highest fluctuations. The “hammer-like” motion of the domain 1- domain 4 of LFs during 100 as the simulation progresses from time step “p” to “n” and to “n + m”. The X-ray structure is overlaid on the MD frames at the t ps (red) and tn ps (green) in ribbon and tn+m ps (gray) in cartoon representation. (GIF 154 kb)

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High resolution image (TIFF 10333 kb)
894_2015_2878_Fig13_ESM.gif (210 kb)
Figure S4

A. The above view of the complex of LFs (surface) and PA63 (ribbons) obtained from the frame MD simulations, LF domains 1 (for clarity domains 2-4 are not shown) and PA domains 1’-4 (purple, navy, brown and green ribbons), B. Interacting amino acids from LF (yellow) and PA (gray). (GIF 210 kb)

894_2015_2878_MOESM4_ESM.tiff (9.3 mb)
High resolution image (TIFF 9472 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.School of Pharmacy, H3423 Health Sciences CentreMemorial University of NewfoundlandSt. John’sCanada
  2. 2.Department of Chemistry, Faculty of ScienceMemorial University of NewfoundlandSt. John’sCanada
  3. 3.Department of Anatomy and Cell Biology, Groupe de recherche axé sur la structure des protéines (GRASP), Groupe d’Étude des Proteines Membranaires (GÉPROM)McGill UniversityMontrealCanada

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