Proteolytic processing of the C terminus of the alpha(1C) subunit of L-type calcium channels and the role of a proline-rich domain in membrane tethering of proteolytic fragments

Although most L-type calcium channel alpha(1C) subunits isolated from heart or brain are similar to 190-kDa proteins that lack similar to 50 kDa of th e C terminus, the C-terminal domain is present in intact cells. To test the hypothesis that the C terminus is processed but remains functionally assoc iated with the channels, expressed, full-length alpha(1C) subunits mere cle aved in vitro by chymotrypsin to generate a 190-kDa C-terminal truncated pr otein and C-terminal fragments of 30-56 kDa, These hydrophilic C-terminal f ragments remained membrane-associated, A C-terminal proline-rich domain (PR D) was identified as the mediator of membrane association. The alpha(1C) PR D bound to SH3 domains in Src, Lyn, Hck, and the channel beta(2) subunit. M utant alpha(1C) Subunits lacking either similar to 50 kDa of the C terminus or the PRD produced increased barium currents through the channels, demons trating that these domains participate in the previously described (Wei, X. , Neely, a., Lacerda, A. E, Olcese, r,, Stefani, E,, Perez-Reges, E., and B irnbaumer, L,, (1994) J. Biol. Chem. 269, 1635-1640) inhibition of channel function by the C terminus.