Stochastic simulation of activation in the G-protein cascade of phototransduction.
Activation of the G-protein cascade underlying phototransduction has been modeled by simulating the two-dimensional diffusional interactions that occur at the rod disc membrane between the three reacting protein species, which are the activated rhodopsin (R*), the G-protein (G), and the effector protein (E, the phosphodiesterase, PDE). The stochastic simulations confirm the main predictions of a simplified analytical model (Lamb, T. D., and E. N. Pugh, 1992, Journal of Physiology 449:719-758), and extend that treatment to more complicated cases, where there is a finite probability of reaction or a finite time for reaction. The simulations also provide quantitative estimates of the efficiency of coupling from activated G-protein (G*) to activated effector (E*) in terms of the concentrations, lateral diffusion coefficients, and binding rate constants of the participating molecules; the efficiency of coupling from G* to E* is found to be not as high as in the previous simplified analytical theory. The findings can be extended to other G-protein cascades, provided that the physical parameters of those cascades are specified.
Lamb
T D
TD
Physiological Laboratory, University of Cambridge, United Kingdom.
D000818:Animals; D004058:Diffusion; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D008961:Models, Structural; D010786:Photoreceptor Cells / Q000502:physiology*; D015398:Signal Transduction; D012984:Software; D013269:Stochastic Processes; D013997:Time Factors
D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins