Slo1 tail domains, but not the Ca2+ bowl, are required for the β1 subunit to increase the apparent Ca2+ sensitivity of BK channels

Xiang Qian, Crina M. Nimigean, Xiaowei Niu, Brenda L. Moss, Karl L. Magleby

Research output: Contribution to journalArticle

38 Scopus citations

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 17β-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.

Original languageEnglish (US)
Pages (from-to)829-843
Number of pages15
JournalJournal of General Physiology
Volume120
Issue number6
DOIs
StatePublished - Dec 1 2002

Keywords

  • Ca-activated K channel
  • DHS-I
  • Estrogen
  • RCK domain
  • Slo3

ASJC Scopus subject areas

  • Physiology

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