Title: Diffusion in nanostructures: Role of interaction potentials Sergey M. Bezrukov Laboratory of Physical and Structural Biology, NICHD National Institutes of Health
1Diffusion in nanostructures Role of interaction
potentials Sergey M. BezrukovLaboratory of
Physical and Structural Biology, NICHDNational
Institutes of Health
together with V. Adrian Parsegian, Alexander M.
Berezhkovskii, Philip A. Gurnev, Ekaterina M.
Nestorovich, Amos B. Oppenheim, and Mathias
Winterhalter
2Sunday, August 26, morning, between 900 and 1000
Alf Honigmann Translocation or not? (A particle
can leave the channel from the side it enters).
Roland Benz Asymmetry? Do you mean
voltage-induced asymmetry?
Boris Shklovskii It is all about linear vs.
non-linear response.
3Channel asymmetry, Maxwells demons, non-linear
response, and all that
4A teaser
?
5Plan of the talk
- Consider the simplest binding-site model
- Show experiments on single l-phage docking to
maltoporin - Introduce and explain the benefits of the
diffusion model (e.g. resolve the teaser)
6The simplest binding site model of ion channel
7The simplest binding site model of ion channel
8The simplest binding site model of ion
channel The flux
9Consider equilibrium
10Translocations vs. returns
11Channel blocked from one side
12Plan of the talk
- Consider the simplest binding-site model
- Show experiments on single l-phage docking to
maltoporin - Introduce and explain the benefits of the
diffusion model (e.g. resolve the teaser)
13Constructing a lipid bilayer
60 m Dia. Hole
A
Lipid Monolayer
15 ? Teflon Film
Electrode
Water Tube
KCl
KCl
Teflon Chamber
14Maltoporin trimeric b-barrel
- Native Maltoporin is a homotrimer
- Each subunit is a 421 a.a. 18 stranded b-barrel
- Loops L4 , L5 and, L6 form a complex near the
extracellular channel vestibule (amino acid
residues relevant for phage binding are shown in
red)
15(No Transcript)
16Effect of phage on the membrane containing
Maltoporin trimers
- Current corresponding to 10 Maltoporin trimers is
reduced by phage at the cis-side addition - Phage addition to the trans-side of the membrane
did not produce any significant changes in the
current
17Ion current and maltohexaose transport in single
Maltoporin trimer
10 pA
Maltohexaose molecules bind to a specific site
inside the pore and transiently block ion current
Ion conductance is stable in the absence of
maltohexaose
18Monitoring the functional properties of the
single Maltoporin trimer embedded into bilayer
cis-
- In the absence of maltohexaose and l phage
Maltoporin trimer is permanently open
trans-
/ 150 mV /
0 mV /
19Monitoring the functional properties of the
single Maltoporin trimer embedded into bilayer
cis-
- Transmembrane current gets transiently blocked
when maltohexaose is applied to the cis-side of
the membrane - Phage was added simultaneously to the same (cis)
side of the membrane
trans-
/ 150 mV /
0 mV /
20Monitoring the functional properties of the
single Maltoporin trimer embedded into bilayer
cis-
- Docking of phage decreases ion conductance and
simultaneously inhibits maltohexaose penetration
in all the three pores of Maltoporin
trans-
/ 150 mV /
0 mV /
21Subsequent application of maltohexaose to the
trans-side produces current fluctuations
cis-
trans-
/ 150 mV /
0 mV /
22Probing the phage-bound state of Maltoporin for
independence of pore blockage Thermodynamics
Binomial distribution probes independence of
blocking events
Pk probability of k (out of 3) blocked pores k
of blocked pores p probability of finding a
single pore blocked p is determined by
equilibrium constant K eq and sugar
(maltohexaose) concentration (C) obtained from
the same current traces
Blocking events are independent
23Phage docking introduces hierarchy in Maltoporin
conductance
Phage-free Maltoporin trimer D 1 D 2 D 3
Phage-bound Maltoporin trimer D 1 lt D 2 lt D 3
D 1
D 1
D 2
D 2
D 3
D 3
maltohexaose trans-side
24Phage introduces a new common pathway for ion
fluxes in Maltoporin
Phage-free Maltoporin
Phage-bound Maltoporin
500 pS
Phage introduces a formation of one common
entryway, connecting the extracellular face of
Maltoporin with the outer membrane solution
25Maltohexaose residence time increases upon phage
binding
Maltohexaose residence time in Maltoporin pore
(at the trans-side sugar application) increases
upon l phage binding This finding suggests that
the phage binding site does not overlap with the
zone of sugar binding
26Phage introduces a new common pathway for ion
fluxes in Maltoporin
27Plan of the talk
- Consider the simplest binding-site model
- Show experiments on single l-phage docking to
maltoporin - Introduce and explain the benefits of the
diffusion model (e.g. resolve the teaser)
28Particle and Channel
29Particle and Channel
30Particle and Channel
31Particle and Channel
32Analytical Approach
33Particle Potential in the Channel
34Computer simulations
L
2a
35Computer simulations
36Particle and Channel
37Free diffusion
Diffusion with 'sticking'
382a
L
39Instead of treating a channel as a featureless
binding site we considered single-particle
dynamics inside its pore
40Flux
Rectangular potential well of depth U0
occupying the entire channel
41Dependence of the flux on the depth (bU) and tilt
(bFl/2) of the potential well
42Which one is more effective?
?
43Introducing entropic potential
44Simulations
45Simulations vs. Theory Entropic Potential
46References
The phage story J. Molecular Biol., 2006,
3591447-1455. Theory Biophys. J., 2005,
88L7-L19 Phys. Rev. Lett., 2006, 97020601 J.
of Physics Condensed Matter, 2007, 19065148 J.
Chem. Phys., 2007 in press.