Back on the complex page, double-click the Galpha complex species to load it for editing. Then, click 'New' at the top of the 'Relations' list on the right and select 'Create/Edit Association'.

Double-click Gbetagamma in the list on the left to select it as the interaction partner for Galpha.

Next, we want to specify that only Galpha in the GDP (not GTP) state can bind to Gbetagamma. To do this, we set the GTP feature tag of Galpha to 'off' by right-click (Mac: control-click) on the feature tag and selecting 'off'. This 'off' state will now be the condition for the association to take place. Note: If we wanted the reaction to have an influence on the state of the resulting complex, we would assign the appropriate states in the result complex (for which we still have to define the species).

To establish the association, draw a line between the 'Gbetagamma binding site' of Galpha and the only binding site of Gbetagamma.

Confirm the creation of a new molecular interaction.

...and build the result complex species.

Specify an association rate (1.0e6) and (optionally, but recommended) a name for the association.

Note, that we do not have to specify explicitly that Galpha keeps its GTP 'off' state when undergoing the association. This is an example for the Simmune Modeler's implicit rule that result complexes (on the 'right-hand side of the reaction') inherit their states from the source complexes ('left-hand side of the reaction') when these are not specified to be different, i.e. when they are set to 'don't care' in the result.

This is the case here for the GTP state of Galpha. According to the rule we specify here iconographically, Galpha has to be in the GTP 'off' state in order to undergo this association. Binding to Gbetagamma, it will then simply keep this state because the GTP tag is set to 'don't care' in the Galpha.Gbetagamma result complex on the association page. We will encounter this implicit rule for the dissociations of Galpha as well.

The file "G_protein_4.7.dbf" represents the model as it should be at this stage of the tutorial.

To define the dissociation click the 'Create Dissociation' button.

Split the interaction between the binding sites and set the off-rate to 0.01 per second. This is a rather slow off-rate, meaning: few of these dissociations happen per unit time. Another way to say this is to state that the complex has a long 'half-life' time (100 seconds, the inverse of the off-rate). To define the dissociation click the 'Create Dissociation' button.

However, only the Galpha molecule in the GDP (not GTP) state will bind Gbetagamma this well. To specify this condition, we set the GTP feature tag on Galpha to 'off' by right-click (Mac: control-click) on the feature tag and selecting 'off'.

Click 'Save' (important!!).

Note that here, again, we have taken advantage of Simmune's implicit rule that unspecified states ('don't care') in reaction results inherit from the source complexes. The result complex Galpha on the right-hand side carries a 'don't care' GTP state tag and so will inherit the GTP 'off' state from the Galpha in the complex on the left.

To specify the (much faster) dissociation of Galpha(GTP) from Gbetagamma, we can simply stay on the dissociation page and edit the dissociation properties (off-rate to 10 per second and GTP tag to 'on'.

Clicking 'Save' again will now prompt a request to specify whether this is meant as an update for the previous definition or whether this will be a new dissociation. It is very important to select 'create a new disssociation' because otherwise the previous one will be replaced with this new specification and will be lost. Note that complexes that don't have dissociations will remain bound indefinitely.

Again taking advantage of Simmune's implicit rule about result complexes with 'don't care' tags inheriting their states from the source complexes, we can use the same result complexes for this second, faster dissociation as we did earlier for the slow dissocaition of Galpha GDP from Gbetagamma.

Go back -- first to the association page...

...then to the page showing the properties of Galpha.

The file "G_protein_4.14.dbf" represents the model as it should be at this stage of the tutorial.