Palmitoylation of STREX domain confers cerebroside sensitivity to the BKCa channel

Our previous study reported that cerebrosides from traditional Chinese medicine Baifuzi directly interact with the STREX domain of BK_Ca channels, which in turn results in the therapeutic effect of Baifuzi on ischemic stroke. However, it is not known how cerebrosides in the plasma membrane could interact with the STREX domain that is in the cytoplasmic side. Using patch-clamp technique, effects of different cerebrosides on the BK_Ca channel were studied by measuring single channel currents in CHO cells expressing wild type or mutated BK_Ca channels. Palmitoylation of the STREX domain was removed either by site-directed mutagenesis or pharmacological inhibition. Removal of palmitoylation sites at C646 and C647 by mutating the residues to Ala abolished the ability of cerebrosides to activate the BK_Ca channel. In contrast, the mutation neither changed the single channel conductance nor voltage sensitivity of the channel. Both palmitoylation inhibitors tunicamycin and palmitic acid analog 2-bromopalmitate attenuated the activation of the BK_Ca channel by cerebrosides. Furthermore, confocal images on STREX-EGFP fragments demonstrated that STREX fragments no longer associated with the plasma membrane when the palmitoylation was removed or blocked. These findings suggest that palmitoylation of the STREX domain is necessary for cerebrosides to activate the BK_Ca channel and provide insight into the mechanism of how Baifuzi could exert therapeutic effect on ischemic stroke.