Skip to main content
NCBI home page
Biophysical Journal logoLink to Biophysical Journal
. 1996 Dec;71(6):3051–3063. doi: 10.1016/S0006-3495(96)79499-7

Stochastic simulation of the transducin GTPase cycle.

S Felber 1, H P Breuer 1, F Petruccione 1, J Honerkamp 1, K P Hofmann 1
PMCID: PMC1233794  PMID: 8968576

Abstract

On rod disc membranes, single photoactivated rhodopsin (R*) molecules catalytically activate many copies of the G-protein (Gt), which in turn binds and activates the effector (phosphodiesterase). We have performed master equation simulations of the underlying diffusional protein interactions on a rectangular 1-micron2 model membrane, divided into 15 x 15 cells. Mono- and bimolecular reactions occur within cells, and diffusional transitions occur between (neighboring) cells. Reaction and diffusion constants yield the related probabilities for the stochastic transitions. The calculated kinetics of active effector form a response that is essentially determined by the stochastic lifetime distribution of R* (with characteristic time tau R*) and the reaction constants of Gt activation. Only a short tau R* (approximately 0.3 s) and a high catalytic rate (3000-4000 Gt s-1 R*-1) are consistent with electrophysiological data. Although R* shut-off limits the rise of the response, the lifetime distribution of free R* is not translated into a corresponding variability of the response peaks, because 1) the lifetime distribution of catalytically engaged R* is distorted, 2) small responses are enlarged by an overshoot of active effector, and 3) larger responses tend to undergo saturation. Comparison of these results to published photocurrent waveforms may open ways to understand the relative uniformity of the rod response.

Full text

PDF
3051

Images in this article

3057FIGURE 2
on p.3057

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Antonny B., Otto-Bruc A., Chabre M., Vuong T. M. GTP hydrolysis by purified alpha-subunit of transducin and its complex with the cyclic GMP phosphodiesterase inhibitor. Biochemistry. 1993 Aug 24;32(33):8646–8653. doi: 10.1021/bi00084a036. [DOI] [PubMed] [Google Scholar]
  2. Baylor D. A., Nunn B. J., Schnapf J. L. The photocurrent, noise and spectral sensitivity of rods of the monkey Macaca fascicularis. J Physiol. 1984 Dec;357:575–607. doi: 10.1113/jphysiol.1984.sp015518. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Bruckert F., Chabre M., Vuong T. M. Kinetic analysis of the activation of transducin by photoexcited rhodopsin. Influence of the lateral diffusion of transducin and competition of guanosine diphosphate and guanosine triphosphate for the nucleotide site. Biophys J. 1992 Sep;63(3):616–629. doi: 10.1016/S0006-3495(92)81650-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Chen J., Makino C. L., Peachey N. S., Baylor D. A., Simon M. I. Mechanisms of rhodopsin inactivation in vivo as revealed by a COOH-terminal truncation mutant. Science. 1995 Jan 20;267(5196):374–377. doi: 10.1126/science.7824934. [DOI] [PubMed] [Google Scholar]
  5. Fung B. K., Hurley J. B., Stryer L. Flow of information in the light-triggered cyclic nucleotide cascade of vision. Proc Natl Acad Sci U S A. 1981 Jan;78(1):152–156. doi: 10.1073/pnas.78.1.152. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Heck M., Hofmann K. P. G-protein-effector coupling: a real-time light-scattering assay for transducin-phosphodiesterase interaction. Biochemistry. 1993 Aug 17;32(32):8220–8227. doi: 10.1021/bi00083a024. [DOI] [PubMed] [Google Scholar]
  7. Kahlert M., Hofmann K. P. Reaction rate and collisional efficiency of the rhodopsin-transducin system in intact retinal rods. Biophys J. 1991 Feb;59(2):375–386. doi: 10.1016/S0006-3495(91)82231-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Kohl B., Hofmann K. P. Temperature dependence of G-protein activation in photoreceptor membranes. Transient extra metarhodopsin II on bovine disk membranes. Biophys J. 1987 Aug;52(2):271–277. doi: 10.1016/S0006-3495(87)83214-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Kühn H., Bennett N., Michel-Villaz M., Chabre M. Interactions between photoexcited rhodopsin and GTP-binding protein: kinetic and stoichiometric analyses from light-scattering changes. Proc Natl Acad Sci U S A. 1981 Nov;78(11):6873–6877. doi: 10.1073/pnas.78.11.6873. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Lagnado L., Baylor D. A. Calcium controls light-triggered formation of catalytically active rhodopsin. Nature. 1994 Jan 20;367(6460):273–277. doi: 10.1038/367273a0. [DOI] [PubMed] [Google Scholar]
  11. Lamb T. D. Gain and kinetics of activation in the G-protein cascade of phototransduction. Proc Natl Acad Sci U S A. 1996 Jan 23;93(2):566–570. doi: 10.1073/pnas.93.2.566. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Lamb T. D., Pugh E. N., Jr A quantitative account of the activation steps involved in phototransduction in amphibian photoreceptors. J Physiol. 1992 Apr;449:719–758. doi: 10.1113/jphysiol.1992.sp019111. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Lamb T. D. Stochastic simulation of activation in the G-protein cascade of phototransduction. Biophys J. 1994 Oct;67(4):1439–1454. doi: 10.1016/S0006-3495(94)80617-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Langlois G., Chen C. K., Palczewski K., Hurley J. B., Vuong T. M. Responses of the phototransduction cascade to dim light. Proc Natl Acad Sci U S A. 1996 May 14;93(10):4677–4682. doi: 10.1073/pnas.93.10.4677. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Liebman P. A., Parker K. R., Dratz E. A. The molecular mechanism of visual excitation and its relation to the structure and composition of the rod outer segment. Annu Rev Physiol. 1987;49:765–791. doi: 10.1146/annurev.ph.49.030187.004001. [DOI] [PubMed] [Google Scholar]
  16. Liebman P. A., Pugh E. N., Jr The control of phosphodiesterase in rod disk membranes: kinetics, possible mechanisms and significance for vision. Vision Res. 1979;19(4):375–380. doi: 10.1016/0042-6989(79)90097-x. [DOI] [PubMed] [Google Scholar]
  17. Palczewski K., Buczylko J., Ohguro H., Annan R. S., Carr S. A., Crabb J. W., Kaplan M. W., Johnson R. S., Walsh K. A. Characterization of a truncated form of arrestin isolated from bovine rod outer segments. Protein Sci. 1994 Feb;3(2):314–324. doi: 10.1002/pro.5560030215. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Pepperberg D. R., Birch D. G., Hofmann K. P., Hood D. C. Recovery kinetics of human rod phototransduction inferred from the two-branched alpha-wave saturation function. J Opt Soc Am A Opt Image Sci Vis. 1996 Mar;13(3):586–600. doi: 10.1364/josaa.13.000586. [DOI] [PubMed] [Google Scholar]
  19. Pepperberg D. R., Cornwall M. C., Kahlert M., Hofmann K. P., Jin J., Jones G. J., Ripps H. Light-dependent delay in the falling phase of the retinal rod photoresponse. Vis Neurosci. 1992 Jan;8(1):9–18. doi: 10.1017/s0952523800006441. [DOI] [PubMed] [Google Scholar]
  20. Pugh E. N., Jr, Lamb T. D. Amplification and kinetics of the activation steps in phototransduction. Biochim Biophys Acta. 1993 Mar 1;1141(2-3):111–149. doi: 10.1016/0005-2728(93)90038-h. [DOI] [PubMed] [Google Scholar]
  21. Pulvermüller A., Palczewski K., Hofmann K. P. Interaction between photoactivated rhodopsin and its kinase: stability and kinetics of complex formation. Biochemistry. 1993 Dec 28;32(51):14082–14088. doi: 10.1021/bi00214a002. [DOI] [PubMed] [Google Scholar]
  22. Schneeweis D. M., Schnapf J. L. Photovoltage of rods and cones in the macaque retina. Science. 1995 May 19;268(5213):1053–1056. doi: 10.1126/science.7754386. [DOI] [PubMed] [Google Scholar]
  23. Vuong T. M., Chabre M. Deactivation kinetics of the transduction cascade of vision. Proc Natl Acad Sci U S A. 1991 Nov 1;88(21):9813–9817. doi: 10.1073/pnas.88.21.9813. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Vuong T. M., Chabre M., Stryer L. Millisecond activation of transducin in the cyclic nucleotide cascade of vision. Nature. 1984 Oct 18;311(5987):659–661. doi: 10.1038/311659a0. [DOI] [PubMed] [Google Scholar]

Articles from Biophysical Journal are provided here courtesy of The Biophysical Society

RESOURCES