G-Protein β-Subunit Specificity in the Fast Membrane-Delimited Inhibition of Ca2+Channels

Open Access
Publisher Website
Google Scholar
Abstract
We investigated which subtypes of G-protein β subunits participate in voltage-dependent modulation of N-type calcium channels. Calcium currents were recorded from cultured rat superior cervical ganglion neurons injected intranuclearly with DNA encoding five different G-protein β subunits. Gβ1and Gβ2strongly mimicked the fast voltage-dependent inhibition of calcium channels produced by many G-protein-coupled receptors. The Gβ5subunit produced much weaker effects than Gβ1and Gβ2, whereas Gβ3and Gβ4were nearly inactive in these electrophysiological studies. The specificity implied by these results was confirmed and extended using the yeast two-hybrid system to test for protein–protein interactions. Here, Gβ1or Gβ2coupled to the GAL4-activation domain interacted strongly with a channel sequence corresponding to the intracellular loop connecting domains I and II of a α1subunit of the class B calcium channel fused to the GAL4 DNA-binding domain. In this assay, the Gβ5subunit interacted weakly, and Gβ3and Gβ4failed to interact. Together, these results suggest that Gβ1and/or Gβ2subunits account for most of the voltage-dependent inhibition of N-type calcium channels and that the linker between domains I and II of the calcium channel α1subunit is a principal receptor for this inhibition.