Interaction of T-Type Calcium Channel Cav3.3 with the β-Subunit

The beta-subunit of high-voltage-activated (HVA) calcium channels is essential for the regulation of expression and gating. On the other hand, various reports have suggested that beta subunits play no role in the regulation of low-voltage-activated T-type channels. In addition there has been no clear demonstration of a physical interaction between the alpha-subunit of T-type channel with beta-subunit. In this study, we systematically investigated the interaction between Ca-v alpha and Ca-v beta. The four Ca-v beta isoforms were expressed in a bacterial system and purified into homogeneity, whereas the ten types of Ca-v alpha alpha interaction domain (AID) peptides were chemically synthesized. All possible combinations of Ca-v alpha and Ca-v beta were then tested for by in vitro immunoassays. We describe here the identification of a new interaction between Ca(v)3.3 and Ca-v beta proteins. This interaction is of low affinity compared to that between the AID of the HVA alpha-subunit and the alpha-binding pocket (ABP) site of the beta-subunit. The AID peptide of HVA channel exerted no effect on the Ca(v)3.3-Ca-v beta interaction, thus demonstrating that another site not in the ABP of Ca-v beta protein played a role in binding with Ca(v)3.3. This is the first demonstration of an alpha-beta subunit interaction in a T-type calcium channel.