Direct inhibition of the interaction between α-interaction domain and β-interaction domain of voltage-dependent Ca2+ channels by gem

The Ras-related small G-protein Gem regulates voltage-dependent Ca2+ channels (VDCCs) through interaction with the beta-subunit of the VDCC. This action of Gem is mediated by regulated alpha(1)-subunit expression at the plasma membrane. In the present study, we examined the mechanism of the inhibition of VDCC activity by Gem. The beta-interaction domain (BID) of the beta-subunit, which specifically interacts with the beta-interaction domain ( AID) of the alpha(1)-subunit, is shown to be essential for the interaction between Gem and beta-subunits. In addition, the AID peptide inhibited interaction between Gem and beta-subunits in a dose-dependent manner. GemS88N mutant, which has low binding affinity for guanine nucleotide, did not interact with beta-subunits, allowing alpha1-subunit expression at the plasma membrane. This inhibitory effect of wild-type Gem on VDCC activity was reduced in cells expressing GemS88N. The overexpression of wild- type Gem in pancreatic beta-cell line MIN6 cells suppressed Ca2+-triggered secretion, whereas overexpression of GemS88N induced Ca2+ -triggered secretion to control level. These results suggest that GTPase activity of Gem is required for the binding of Gem to BID that regulates VDCC activity through interaction with AID.