G-proteins are heterotrimers, consisting of an α, β, and γ subunit. They are involved in signal transduction for a number of types of ligands such as hormones, neurotransmitters and chemokines. These extracellular signals are received by members of a large superfamily of receptors, the GPCRs, that activate the G-proteins, which then route the signals to several distinct intracellular signaling pathways thus initiating changes in cell behavior. In the inactive heterotrimeric state, GDP is bound to the G-α subunit. Upon activation, GDP is released, GTP binds to G-α, and subsequently G-α-GTP dissociates from the G-βγ heterodimer and from the receptor...