Identification and functional characterization of ankyrin-repeat family protein ANKRA as a protein interacting with BKCa channel.

Ankyrin-repeat family A protein (ANKRA) was originally cloned in mouse as an interacting protein to megalin, a member of low-density lipoprotein receptor superfamily. Here, we report that the isolation of rat ANKRA as a new binding partner for the alpha-subunit of rat large-conductance Ca2+-activated K+ channel (rSlo). We mapped the binding region of each protein by using yeast two-hybrid and in vitro binding assays. ANKRA expressed together with rSlo channels were colocalized near the plasma membrane and coimmunoprecipitated in transfected cells. We also showed that BKCa channel in rat cerebral cortex coprecipitated with rANKRA and colocalized in cultured rat hippocampal neuron. Although the coexpression of ANKRA did not affect the surface expression of rSlo, the gating kinetics of rSlo channel was significantly altered and the effects were highly dependent on the intracellular calcium. These results indicate that ANKRA could modulate the excitability of neurons by binding directly to endogenous BKCa channel and altering its gating kinetics in a calcium-dependent manner.