Role of the C terminus of the alpha(1C) (Ca(v)1.2) subunit in membrane targeting of cardiac L-type calcium channels

We have previously demonstrated that formation of a complex between L-type calcium (Ca2+) channel alpha(1C) (Ca(V)1.2) and beta subunits was necessary to target the channels to the plasma membrane when expressed in tsA201 cel ls. In the present study, we identified a region in the C terminus of the a lpha(1C) subunit that was required for membrane targeting. Using a series o f C-terminal deletion mutants of the alpha(1C) subunit, a domain consisting of amino acid residues 1623-1666 ("targeting domain") in the C terminus of the alpha(1C) subunit has been identified to be important for correct targ eting of L-type Ca2+ channel complexes to the plasma membrane. Although cel ls expressing the wild-type alpha(1C) and beta(2a) subunits exhibited punct ate clusters of channel complexes along the plasma membrane with little int racellular staining, co-expression of deletion mutants of the alpha(1C) sub unit that lack the targeting domain with the beta(2a) subunit resulted in a n intracellular localization of the channels. In addition, three other regi ons in the C terminus of the alpha(1C) subunit that were downstream of resi dues 1623-1666 were found to contribute to membrane targeting of the L-type channels. Deletion of these domains in the alpha(1C) subunit resulted in a reduction of plasma membrane-localized channels, and a concomitant increas e in channels localized intracellularly, Taken together, these results have demonstrated that a targeting domain in the C terminus of the alpha(1C) su bunit was required for proper plasma membrane localization of the L-type Ca 2+ channels.