Direct binding of G-protein beta gamma complex to voltage-dependent calcium channels

Voltage-dependent Ca2+ channels play a central role in controlling neurotransmitter release at the synapse(1,2). They can be inhibited by certain G-protein-coupled receptors, acting by a pathway intrinsic to the membrane(3-6). Here we show that this inhibition results from a direct interaction between the G-protein beta gamma complex and the pore-forming alpha(1) subunits of several types of these channels(7). The interaction is mediated by the cytoplasmic linker connecting the first and second transmembrane repeats. Within this linker, binding occurs both in the alpha(1) interaction domain (AID)(8), which also mediates the interaction between the alpha(1) and beta subunits of tbe channel, and in a second downstream sequence. Further analysis of the binding site showed that several amino-terminal residues in the AID are critical for G beta gamma binding, defining a site distinct from the carboxy-terminal residues shown to be essential for binding the beta-subunit of the Ca2+ channel(9). Mutation of an arginine residue within the N-terminal motif abolished beta gamma binding and rendered the channel refractory to G-protein modulation when expressed in Xenopus oocytes, showing that the interaction is indeed responsible for G-protein-dependent modulation of Ca2+ channel activity.