Transcript Possible optoelectronic applications of Bacteriorhodopsin

Electric signals to reveal ion
pump function
András Dér
Biological Research Center of the Hungarian Academy of
Sciences
Institute of Biophysics
P. O. B. 521, H-6701 Szeged, Hungary
Electric signals
Crucial role in life functions:
Signal and energy transduction
Signal transduction
Propagation of the nerve impulse
Hodgkin, Huxley, Katz
Nobel prize (1963)
Energy transduction
mitochondrial
electron transfer
chemiosmosis: P. Mitchell, Nobel prize, 1978
ATP-ase: Boyer, Walker, Skou, Nobel prize, 1997
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
How to measure electric signals?
Patch clamp; Nobel prize 1991: Neher and Sackmann
Microelectrode techniques fail for most pump proteins
Alternative methods. Prerequisite: electrically asymmetric
sample
1. Surface methods
BLM method (Dancsházy et al., 1976; Bamberg et al., 1980)
SSM method (Fendler et al., 1992)
Advantage: ion specificity
Disadvantage: limited spatio-temporal information
2. Bulk methods
Suspension method
Gel method
Dried samples
(Keszthelyi and Ormos, 1980)
(Dér et al., 1985)
(Nagy, 1978; Váró, 1983)
Advantageous for kinetic experiments
Bacteriorhodopsin
bR plays a model role among iontransporting membrane proteins
stability, absorption changes, photoelectric effects
Gel method
cont. light source
monochromator
(mirror)
electrodes
exciting laser
polarizer
sample
detector
transient recorder
trigger
amplifier
computer
input 1
(mirror)
input 2
monochromator
detector
Correlation between electric and optical signals
d
 (t ) ~   xi (t )
dt
i
k
k
i
Conditions: speed, linearity,
insensitivity to geometric details
Modeling the electrolyte

E
B
ri  ri  ri
 
E
r i  i qi E(ri )t
B
SD 
ri   i  rk ek
k
Ionic relaxation
1400
1200
+
Concentration (a.u.)
Na
1000
800
600
400
bulk
200
-
Cl
0
0.0
0.5
1.0
1.5
Time (µs)
2.0
2.5
3.0
Properties of ionic relaxation
1. speed
2. anisotropy (F)
3. linearity (E)
4. insensitivity to geometric
details (B,C,D)
Temporal superposition solved
d
 (t ) ~  
xi (t )
dt
i
k
k
i
u k (t )   k (t )  ik
How can we use this?
q
q
0k
q
q
1k
 2k
…
dk
… nk  0k  qd k
Detection of the 3D electric signals
Dér et al. (1999)
Testing MD models
Measurement
Model
The function of a bR molecule
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)
Acknowledgements
Lajos Keszthelyi
Stefka Taneva
Pál Ormos
Sofia
György Váró
Sándor Suhai
Rudolf Tóth-Boconádi
Nicoleta Bondar
László Oroszi
Heidelberg
László Fábián
Walther Stoeckenius
Szeged
San Francisco