Determinants of the voltage dependence of G protein modulation within calcium channel β subunits

• Published in: Pflügers Archiv 2009-02, Vol.457 (4), p.743-756
• Main Authors: Dresviannikov, Andriy V., Page, Karen M., Leroy, Jerôme, Pratt, Wendy S., Dolphin, Annette C.
• Format: Article
• Language: English
• Subjects: Animals; Biomedical and Life Sciences; Biomedicine; Calcium Channels - genetics; Calcium Channels - metabolism; Cell Biology; GTP-Binding Proteins - genetics; GTP-Binding Proteins - metabolism; Human Physiology; Ion Channel Gating - physiology; Ion Channels; Ion Channels, Receptors and Transporters; Molecular Medicine; Neurosciences; Patch-Clamp Techniques; Protein Structure, Tertiary; Protein Subunits - genetics; Protein Subunits - metabolism; Receptors; Receptors and Transporters; Two-Hybrid System Techniques
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s00424-008-0549-7

Ca V β subunits of voltage-gated calcium channels contain two conserved domains, a src -homology-3 (SH3) domain and a guanylate kinase-like (GK) domain with an intervening HOOK domain. We have shown in a previous study that, although Gβγ-mediated inhibitory modulation of Ca V 2.2 channels did not require the interaction of a Ca V β subunit with the Ca V α1 subunit, when such interaction was prevented by a mutation in the α1 subunit, G protein modulation could not be removed by a large depolarization and showed voltage-independent properties (Leroy et al., J Neurosci 25:6984–6996, 2005 ). In this study, we have investigated the ability of mutant and truncated Ca V β subunits to support voltage-dependent G protein modulation in order to determine the minimal domain of the Ca V β subunit that is required for this process. We have coexpressed the Ca V β subunit constructs with Ca V 2.2 and α 2 δ-2, studied modulation by the activation of the dopamine D2 receptor, and also examined basal tonic modulation. Our main finding is that the Ca V β subunit GK domains, from either β1b or β2, are sufficient to restore voltage dependence to G protein modulation. We also found that the removal of the variable HOOK region from β2a promotes tonic voltage-dependent G protein modulation. We propose that the absence of the HOOK region enhances Gβγ binding affinity, leading to greater tonic modulation by basal levels of Gβγ. This tonic modulation requires the presence of an SH3 domain, as tonic modulation is not supported by any of the Ca V β subunit GK domains alone.