Assembly and disassembly kinetics of anthrax toxin complexes
Kenneth A Christensen1, Bryan A Krantz, R John Collier
1Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
Biochemistry
|February 16, 2006
Summary
The protective antigen (PA) heptameric prepore of anthrax toxin is highly stable, disassembling over 7 days. This stability, due to subunit cooperation, is crucial for toxin pore formation and cellular entry.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Anthrax toxin's protective antigen (PA) activates proteolytically.
- Activated PA self-associates into a heptameric prepore, [PA(63)](7).
- [PA(63)](7) binds lethal factor (LF) and edema factor (EF) for cellular entry.
Purpose of the Study:
- To investigate the assembly and disassembly kinetics of the anthrax toxin prepore complex.
- To elucidate the role of subunit interactions in prepore stability.
- To understand the effect of LF(N) on PA prepore assembly.
Main Methods:
- Fluorescent labeling of PA with donor and acceptor dyes.
- Förster resonance energy transfer (FRET) to measure kinetics.
- Analysis of dissociation rates for [PA(63)](7) and a ternary complex.
Main Results:
- The [PA(63)](7) prepore exhibits slow disassembly (t(1/2) ≈ 7 days).
- A ternary complex with non-oligomerizing PA mutants rapidly dissociates (t(1/2) ≈ 1 min).
- Cooperative interactions among heptameric subunits significantly enhance prepore stability.
- Low LF(N) concentrations promote prepore assembly; high concentrations inhibit it.
Conclusions:
- The heptameric structure of [PA(63)](7) confers substantial stability through subunit cooperation.
- Prepore stability is critical for anthrax toxin pore formation and function.
- LF(N) concentration modulates PA prepore and ternary complex assembly dynamics.
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