Slo1 Tail Domains, but Not the Ca2+ Bowl, Are Required for the β1 Subunit to Increase the Apparent Ca2+ Sensitivity of BK Channels
Open Access
- 25 November 2002
- journal article
- research article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 120 (6), 829-843
- https://doi.org/10.1085/jgp.20028692
Abstract
Functional large-conductance Ca2+- and voltage-activated K+ (BK) channels can be assembled from four α subunits (Slo1) alone, or together with four auxiliary β1 subunits to greatly increase the apparent Ca2+ sensitivity of the channel. We examined the structural features involved in this modulation with two types of experiments. In the first, the tail domain of the α subunit, which includes the RCK2 (regulator of K+ conductance) domain and Ca2+ bowl, was replaced with the tail domain of Slo3, a BK-related channel that lacks both a Ca2+ bowl and high affinity Ca2+ sensitivity. In the second, the Ca2+ bowl was disrupted by mutations that greatly reduce the apparent Ca2+ sensitivity. We found that the β1 subunit increased the apparent Ca2+ sensitivity of Slo1 channels, independently of whether the α subunits were expressed as separate cores (S0-S8) and tails (S9-S10) or full length, and this increase was still observed after the Ca2+ bowl was mutated. In contrast, β1 subunits no longer increased Ca2+ sensitivity when Slo1 tails were replaced by Slo3 tails. The β1 subunits were still functionally coupled to channels with Slo3 tails, as DHS-I and 17 β-estradiol activated these channels in the presence of β1 subunits, but not in their absence. These findings indicate that the increase in apparent Ca2+ sensitivity induced by the β1 subunit does not require either the Ca2+ bowl or the linker between the RCK1 and RCK2 domains, and that Slo3 tails cannot substitute for Slo1 tails. The β1 subunit also induced a decrease in voltage sensitivity that occurred with either Slo1 or Slo3 tails. In contrast, the β1 subunit–induced increase in apparent Ca2+ sensitivity required Slo1 tails. This suggests that the allosteric activation pathways for these two types of actions of the β1 subunit may be different.Keywords
This publication has 68 references indexed in Scilit:
- Multiple regulatory sites in large-conductance calcium-activated potassium channelsNature, 2002
- The open pore conformation of potassium channelsNature, 2002
- Crystal structure and mechanism of a calcium-gated potassium channelNature, 2002
- A neuronal β subunit (KCNMB4) makes the large conductance, voltage- and Ca 2+ -activated K + channel resistant to charybdotoxin and iberiotoxinProceedings of the National Academy of Sciences, 2000
- A novel calcium-sensing domain in the BK channelBiophysical Journal, 1997
- An Evolutionarily Conserved Binding Site for Serine Proteinase Inhibitors in Large Conductance Calcium-Activated Potassium Channels,Biochemistry, 1996
- Calcium-activated potassium channels expressed from cloned complementary DNAsNeuron, 1992
- Reconstitution in planar lipid bilayers of a Ca2+-dependent K+ channel from transverse tubule membranes isolated from rabbit skeletal muscle.Proceedings of the National Academy of Sciences, 1982
- Single channel recordings of Ca2+-activated K+ currents in rat muscle cell cultureNature, 1981
- Ca-dependent K channels with large unitary conductance in chromaffin cell membranesNature, 1981