Simulating the G-protein cAMP pathway with a two-compartment reactive lattice gas

Cellular signaling (or signal transduction) is the process by which extracellular signals are converted into cellular responses. Mathematical models of signaling pathways may help understanding their general regulatory principles, as well as the roles of the different components often involved in more than one pathway. The aim of the present work is to describe a discrete model in time and space to study the dynamics of the population of molecules involved in a specific pathway. To this purpose, we use a multi-compartment stochastic cellular automaton to simulate one of the best understood cell signaling pathways: the GPCR-pathway. We then show the effect on the signal-carrying ef ciency of condensing a molecular species, which is pivotal to the reaction pathway, in a closed region of the cytosol. We nd that localization increases the robustness of the translocation mechanism only above a density threshold. For homogeneous settings, by increasing the concentration above a critical value, the translocation is obstructed by mere physical occupation constraints of the signal-carrying molecule. This conclusion is in line with previous findings, according to which in highly dense regions of the cytosol, convection by autocatalytic activation of adjacent molecules might be more ef cient than diffusion as a main signal propagation mechanism.