A model of anthrax toxin lethal factor bound to protective antigen

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Anthrax toxin comprises edema factor (EF), lethal factor (LF), and protective antigen (PA).
• PA heptamerizes upon activation, binds EF/LF, and forms a pore for host cell entry.
• Understanding LF-PA interactions is crucial for developing antiterrorism therapeutics.

Purpose of the Study:

• To identify and characterize the specific contact points between LF and PA.
• To generate a reliable structural model of the LF-PA complex.
• To elucidate the mechanism of anthrax toxin translocation into host cells.

Main Methods:

• Directed mutagenesis to identify LF-PA contact sites, including disulfide crosslinking and charge-reversal mutations.
• Rosetta protein-protein docking to predict the lowest energy LF-PA complex structure.
• Biochemical and computational approaches combined to model large protein complexes.

Main Results:

• Three critical LF-PA contact points were identified: one disulfide crosslink and two charge-reversal mutation pairs.
• These experimentally determined contact points align with the lowest energy complex predicted by Rosetta docking.
• The model reveals a highly electrostatic interface for EF/LF binding to PA.
• The N-terminal regions of EF and LF are positioned at the PA pore entrance, ready for translocation.

Conclusions:

• Biochemical and computational methods effectively model large protein complexes like anthrax toxin.
• The identified LF-PA interactions and binding interface provide insights into toxin entry.
• This structural understanding can inform the design of novel therapeutic interventions against anthrax.