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Possible optoelectronic applications of Bacteriorhodopsin

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Possible optoelectronic applications of Bacteriorhodopsin Powered By Docstoc
					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   (Keszthelyi and Ormos, 1980)

Gel method               (Dér et al., 1985)

Dried samples       (Nagy, 1978; Váró, 1983)




 Advantageous for kinetic experiments
Bacteriorhodopsin
bR plays a model role among ion-
 transporting 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 ) ~  
                   k
                               i
                                k
                                  xi (t )
                           i   dt


Conditions: speed, linearity,
insensitivity to geometric details
Modeling the electrolyte


                       E    B
                 ri  ri  ri

                  E           
                 r i  i qi E(ri )t
                                   
                 ri B   i  rkSD ek
                             k
Ionic relaxation



                                          1400


                                          1200
                                                                                                +
                                                                                       Na
                                          1000




                   Concentration (a.u.)
                                          800


                                          600


                                          400
                                                       bulk

                                          200
                                                                                            -
                                                                                      Cl
                                            0
                                                 0.0   0.5    1.0      1.5      2.0   2.5           3.0

                                                                    Time (µs)
   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 ) ~  
                  k
                               i
                                k
                                 xi (t )
                          i   dt
                        u k (t )   k (t )   ik
How can we use this?
                                q
                 q
       q              …             dk
q

 0k       1k   2
                  k
                      …  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

				
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