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A kinetic analysis of protein transport through the anthrax toxin channel.

Basilio D, Kienker PK, Briggs SW, Finkelstein A - J. Gen. Physiol. (2011)

Bottom Line: As expected, the translocation rate is slower with more than one LF(N) bound.We also present a simple electrodiffusion model of translocation in which LF(N) is represented as a charged rod that moves subject to both Brownian motion and an applied electric field.The cumulative distribution of first-passage times of the rod past the end of the channel displays S-shaped kinetics with a voltage dependence in agreement with experimental data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA. dab2043@-med.cornell.edu

ABSTRACT
Anthrax toxin is composed of three proteins: a translocase heptameric channel, (PA(63))(7), formed from protective antigen (PA), which allows the other two proteins, lethal factor (LF) and edema factor (EF), to translocate across a host cell's endosomal membrane, disrupting cellular homeostasis. (PA(63))(7) incorporated into planar phospholipid bilayer membranes forms a channel capable of transporting LF and EF. Protein translocation through the channel can be driven by voltage on a timescale of seconds. A characteristic of the translocation of LF(N), the N-terminal 263 residues of LF, is its S-shaped kinetics. Because all of the translocation experiments reported in the literature have been performed with more than one LF(N) molecule bound to most of the channels, it is not clear whether the S-shaped kinetics are an intrinsic characteristic of translocation kinetics or are merely a consequence of the translocation in tandem of two or three LF(N)s. In this paper, we show both in macroscopic and single-channel experiments that even with only one LF(N) bound to the channel, the translocation kinetics are S shaped. As expected, the translocation rate is slower with more than one LF(N) bound. We also present a simple electrodiffusion model of translocation in which LF(N) is represented as a charged rod that moves subject to both Brownian motion and an applied electric field. The cumulative distribution of first-passage times of the rod past the end of the channel displays S-shaped kinetics with a voltage dependence in agreement with experimental data.

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The fit of the drift-diffusion model to the translocation kinetics of a single His6-LFN molecule. Drift-diffusion model, blue curve; single His6-LFN molecule, red curve. The red curve is the same as that in Fig. 7, except that the time axis has been normalized by the half-time.
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fig8: The fit of the drift-diffusion model to the translocation kinetics of a single His6-LFN molecule. Drift-diffusion model, blue curve; single His6-LFN molecule, red curve. The red curve is the same as that in Fig. 7, except that the time axis has been normalized by the half-time.

Mentions: We next used the drift-diffusion model to quantitate the sigmoidal shape of the translocation kinetics. The single His6-LFN (18% block) macroscopic data at 50 mV from Fig. 7 are replotted in Fig. 8 (red curve) with the time axis normalized by the half-time. The superimposed blue curve is the cumulative first-passage time distribution W(Ω, t′) calculated for Ω = 6.


A kinetic analysis of protein transport through the anthrax toxin channel.

Basilio D, Kienker PK, Briggs SW, Finkelstein A - J. Gen. Physiol. (2011)

The fit of the drift-diffusion model to the translocation kinetics of a single His6-LFN molecule. Drift-diffusion model, blue curve; single His6-LFN molecule, red curve. The red curve is the same as that in Fig. 7, except that the time axis has been normalized by the half-time.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3105512&req=5

fig8: The fit of the drift-diffusion model to the translocation kinetics of a single His6-LFN molecule. Drift-diffusion model, blue curve; single His6-LFN molecule, red curve. The red curve is the same as that in Fig. 7, except that the time axis has been normalized by the half-time.
Mentions: We next used the drift-diffusion model to quantitate the sigmoidal shape of the translocation kinetics. The single His6-LFN (18% block) macroscopic data at 50 mV from Fig. 7 are replotted in Fig. 8 (red curve) with the time axis normalized by the half-time. The superimposed blue curve is the cumulative first-passage time distribution W(Ω, t′) calculated for Ω = 6.

Bottom Line: As expected, the translocation rate is slower with more than one LF(N) bound.We also present a simple electrodiffusion model of translocation in which LF(N) is represented as a charged rod that moves subject to both Brownian motion and an applied electric field.The cumulative distribution of first-passage times of the rod past the end of the channel displays S-shaped kinetics with a voltage dependence in agreement with experimental data.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, NY 10461, USA. dab2043@-med.cornell.edu

ABSTRACT
Anthrax toxin is composed of three proteins: a translocase heptameric channel, (PA(63))(7), formed from protective antigen (PA), which allows the other two proteins, lethal factor (LF) and edema factor (EF), to translocate across a host cell's endosomal membrane, disrupting cellular homeostasis. (PA(63))(7) incorporated into planar phospholipid bilayer membranes forms a channel capable of transporting LF and EF. Protein translocation through the channel can be driven by voltage on a timescale of seconds. A characteristic of the translocation of LF(N), the N-terminal 263 residues of LF, is its S-shaped kinetics. Because all of the translocation experiments reported in the literature have been performed with more than one LF(N) molecule bound to most of the channels, it is not clear whether the S-shaped kinetics are an intrinsic characteristic of translocation kinetics or are merely a consequence of the translocation in tandem of two or three LF(N)s. In this paper, we show both in macroscopic and single-channel experiments that even with only one LF(N) bound to the channel, the translocation kinetics are S shaped. As expected, the translocation rate is slower with more than one LF(N) bound. We also present a simple electrodiffusion model of translocation in which LF(N) is represented as a charged rod that moves subject to both Brownian motion and an applied electric field. The cumulative distribution of first-passage times of the rod past the end of the channel displays S-shaped kinetics with a voltage dependence in agreement with experimental data.

Show MeSH
Related in: MedlinePlus