Abstract
Large-conductance Ca2+- and voltage-activated potassium (BK) channels are widely expressed in tissues. As a voltage and calcium sensor, BK channels play significant roles in regulating the action potential frequency, neurotransmitter release, and smooth muscle contraction. After associating with the auxiliary β2 subunit, mammalian BK(β2) channels (mouse or human Slo1/β2) exhibit enhanced activation and complete inactivation. However, how the β2 subunit modulates the Drosophila Slo1 channel remains elusive. In this study, by comparing the different functional effects on heterogeneous BK(β2) channel, we found that Drosophila Slo1/β2 channel exhibits “paralyzed”-like and incomplete inactivation as well as slow activation. Further, we determined three different modulations between mammalian and Drosophila BK(β2) channels: 1) dSlo1/β2 doesn’t have complete inactivation. 2) β2(K33,R34,K35) delays the dSlo1/Δ3-β2 channel activation. 3) dSlo1/β2 channel has enhanced pre-inactivation than mSlo1/β2 channel. The results in our study provide insights into the different modulations of β2 subunit between mammalian and Drosophila Slo1/β2 channels and structural basis underlie the activation and pre-inactivation of other BK(β) complexes.
Highlights
Large-conductance Ca2+- and voltage-activated potassium (MaxiK or BK) channels are widely distributed in mammalian tissues [1]
Our previous study has demonstrated that in human embryonic kidney (HEK) 293 cell expression system, the α:β2 transfection ratio at 1:0.2 was good enough to maintain saturate β2 binding for every mSlo1/β2 channel
These results indicate that the inactivation ball FIW in the dSlo1/β2 channel might serve as a retention signal that could block the binding of β2
Summary
Large-conductance Ca2+- and voltage-activated potassium (MaxiK or BK) channels are widely distributed in mammalian tissues [1]. Each α subunit has seven transmembrane segments S0–S6 with an extracellular N-terminus and a large cytoplasmic C-terminus, which contains a mechanical linker (C-linker) [16] and two Rossmann-fold Regulator of Conductance of K+ (RCK) domains with two Ca2+ binding sites (calcium bowl and Slo (D367, E535)) that are required for activation by calcium [2, 17,18,19,20]. A passive spring model was proposed as the mechanism whereby the length of the C-linker influenced the BK channel activation and gating [16]. As a unique structure located between the RCK domain and the pore domain (PD) [33], it is possible that the C-linker and AC region are responsible for transferring the mechanical Ca2+ gating force from the RCK domain to the PD
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