Bk Channel C-Linker And Ac Region Are Crucial For Auxiliary Beta 2 Subunit Regulations

Large-conductance Ca2+ and voltage-activated potassium (BK) channels are widely expressed among tissues. As a voltage and calcium sensor, BK channels play significant roles in regulating action potential frequency, neurotransmitter release and smooth muscle contraction. After associating with auxiliary β2 subunit, mammalian BK(β2) channels (mouse or human Slo1/β2) show enhanced activation and complete inactivation through a preinactivated state, while Drosophila Slo1/β2 shows not enhanced but slow activation, “paralyzed” like and incomplete inactivation. However, the structural basis of these unique modulations remains elusive. By comparing the differential regulation of β2 on heterogeneous BK channels, here we demonstrated that C-linker and AC region are critical for β2 regulations. The differences in positively charged residue configurations of C-linker and AC region allow negatively charged β2(D16,E17) interact with different residues of mammalian and Drosophila Slo1 to form different pre-inactivation (PI) sites. Although dSlo1/β2 possesses the same Ca2+ bowl enhancing (ECaB) site and enhancing activation (E) site as mammalian Slo1/β2, different microstructures of C-linker and AC region may abolish the Ca2+ sensitivity enhancing pathway. These results emphasize the functional importance of C-linker and AC region in BK(β2) regulation and may help to understand the mechanisms of activation and inactivation of other BK(β) complexes.