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

Abstract

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 βλ complex and the pore-forming α₁ subunits of several types of these channels⁷. The interaction is mediated by the cytoplasmic linker connecting the first and second transmembrane repeats. Within this linker, binding occurs both in the α₁ interaction domain (AID)⁸, which also mediates the interaction between the α₁ and β subunits of the 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 Gβλ binding, defining a site distinct from the carboxy-terminal residues shown to be essential for binding the β-subunit of the Ca²⁺ channel⁹. Mutation of an arginine residue within the N-terminal motif abolished βλ 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.