GAP Specificity To G Proteins
In general, GAPs tend to be pretty specific for their target G proteins. The exact mechanism of target specificity is not fully known, but it is likely that this specificity comes from a variety of factors. At the most basic level, GAP-to-G protein specificity may come simply from the timing and location of protein expression. RGS9-1, for example, is specifically expressed in the rod and cone photoreceptors in the eye retina, and is the only one to interact with G proteins involved in phototransduction in this area. A certain GAP and a certain G protein happen to be expressed in the same time and place, and that is how the cell ensures specificity. Meanwhile, scaffold proteins can also sequester the proper GAP to its G protein and enhance the proper binding interactions. These binding interactions may be specific for a particular GAP and G protein. Also, GAPs may have particular amino acid domains that only recognize a particular G protein. Binding to other G proteins may not have the same favorable interactions, and they therefore do not interact. GAPs can therefore regulate specific G proteins.
Read more about this topic: GTPase-activating Protein
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