E lectric signals to reveal ion pump function
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Transcript of E lectric signals to reveal ion pump function
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Electric signals to reveal ion pump function
Biological Research Center of the Hungarian Academy of Biological Research Center of the Hungarian Academy of SciencesSciences
Institute of BiophysicsInstitute of Biophysics
P. O. B. 521, H-6701 Szeged, HungaryP. O. B. 521, H-6701 Szeged, Hungary
András DérAndrás Dér
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Electric signals
Crucial role in life functions:
Signal and energy transduction
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Nobel prize (1963)
Hodgkin, Huxley, Katz
Signal transduction
Propagation of the nerve impulse
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chemiosmosis: P. Mitchell, Nobel prize, 1978
ATP-ase: Boyer, Walker, Skou, Nobel prize, 1997
mitochondrial electron transfer
Energy transduction
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Why should we measure electric signals?
Direct information about kinetics, ion specificity
Together with other methods: details of the molecular mechanism is expected to
be revealed
Physicist's approach: atomic level description
- chance to design molecules for biotechnology
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How to measure electric signals?
Microelectrode techniques fail for most pump proteins
Patch clamp; Nobel prize 1991: Neher and Sackmann
Alternative methods. Prerequisite: electrically asymmetric sample
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1. Surface methodsBLM method (Dancsházy et al., 1976; Bamberg et al., 1980)
SSM method (Fendler et al., 1992)
Advantage: ion specificity
Disadvantage: limited spatio-temporal information
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2. Bulk methods
Advantageous for kinetic experiments
Suspension method (Keszthelyi and Ormos, 1980)
Gel method (Dér et al., 1985)
Dried samples (Nagy, 1978; Váró, 1983)
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Bacteriorhodopsin
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bR plays a model role among ion-transporting membrane proteins
stability, absorption changes, photoelectric effects
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polarizerexciting laser
sample detector transient recorder
computer
trigger
input 1
input 2
amplifier
electrodes
detectormonochromator
monochromatorcont. light source(mirror)
(mirror)
Gel method
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Correlation between electric and optical signals
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)(~)( txdt
dt i
i
ki
k
Conditions: speed, linearity, insensitivity to geometric details
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Bi
Eii rrr
trEqr iiiiE )(
k
kSDki
Bi err
Modeling the electrolyte
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0.0 0.5 1.0 1.5 2.0 2.5 3.00
200
400
600
800
1000
1200
1400
bulk
Na+
Cl-
Con
cent
ratio
n (a
.u.)
Time (µs)
Ionic relaxation
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Properties of ionic relaxation
1. speed
2. anisotropy (F)
3. linearity (E)
4. insensitivity to geometric details (B,C,D)
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Temporal superposition solved
)(~)( txdt
dt i
i
ki
k
ki
kk ttu )()(
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How can we use this?
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k0 k
1 k2 kkk
n qd 0
kdq q
q
q
…
…
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Detection of the 3D electric signals
Dér et al. (1999)
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Measurement Model
Testing MD models
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The function of a bR molecule
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Further application examples of the bulk methods
Cl- pumping
(halorhodopsin, bacteriorhodopsin)
Signal transduction
(Chlamydomonas rhodopsin, squid rhodopsin)
Primary processes of photosynthesis
(plant and bacterial photosynthetic reaction centers)
Bioelectronics - fast photodiode, motion sensitive camera
(bacteriorhodospin)
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Acknowledgements
Lajos Keszthelyi
Pál Ormos
György Váró
Rudolf Tóth-Boconádi
László Oroszi
László Fábián
Szeged
Stefka Taneva
Sofia
Sándor Suhai
Nicoleta Bondar
Heidelberg
Walther Stoeckenius
San Francisco