This tutorial will introduce you to some of the essential functionalities of the Simmune Modeler.

You will learn how to create a model specifying molecular interactions and multi-molecular complexes along with associations, dissociations and transformation those complexes can undergo.

G protein coupled receptor (GPCR) signaling is one of the most important mechanisms in cell physiology, playing essential roles for phenomena as diverse as vision, pathogen sensing in the immune system and directed cell migration (chemotaxis). Ligation of the extracellular domain of the receptor renders the cytosolic part of the receptor available for interaction with heterotrimeric G proteins, consisting of three subunits, Galpha, Gbeta and Ggamma. In our model, we will assume that Gbeta and -gamma form a stable complex, Gbetagamma, but the strength of association with the Galpha subunit depends on whether Galpha is bound to guanosine triphosphate (GTP) or -diphosphate (GDP). The activated receptor can catalyze the GDP -> GTP exchange at Galpha, causing a rapid dissociation of Gbetagamma from Galpha. Free Gbetagamma and GTP-Galpha interact with signaling molecules in the cytoplasm or at the inner membrane leaflet, thereby propagating the receptor ligation signal into the cell. Galpha has an "auto-GTPase" activity, allowing it to deactivate itself and then reassociate with Gbetagamma and start the cycle of receptor catalyzed activation again.