The C-terminus of human Cav2.3 voltage-gated calcium channel interacts with alternatively spliced calmodulin-2 expressed in two human cell lines

Abstract

Cav2.3 containing voltage-activated Ca2+ channels are expressed in excitable cells and trigger neurotransmitter and peptide-hormone release. Their expression remote from the fast release sites leads to the accumulation of presynaptic Ca2+ which can both, facilitate and inhibit the influx of Ca2+ ions through Cav2.3. The facilitated Ca2+ influx was recently related to hippocampal postsynaptic facilitation and long term potentiation. To analyze Ca2+ mediated modulation of cellular processes more in detail, protein partners of the carboxy terminal tail of Cav2.3 were identified by yeast-2-hybrid screening, leading in two human cell lines to the detection of a novel, extended and rarely occurring splice variant of calmodulin-2 (CaM-2), called CaM-2-extended (CaM-2-ext). CaM-2-ext interacts biochemically with the C-terminus of Cav2.3 similar to the classical CaM-2 as shown by co-immunoprecipitation. Functionally, only CaM-2-ext reduces whole cell inward currents significantly. The insertion of the novel 46 nts long exon and the consecutive expression of CaM-2-ext must be dependent on a new upstream translation initiation site which is only rarely used in the tested human cell lines. The structure of the N-terminal extension is predicted to be more hydrophobic than the remaining CaM-2-ext protein, suggesting that it may help to dock it to the lipophilic membrane surrounding.