|
|
|
|
|
|
|
||
Address correspondence to Dr. Karl L. Magleby, Department of Physiology and Biophysics, University of Miami School of Medicine, P.O. Box 016340, Miami, FL 33101-6430. E-mail: kmagleby{at}miami.edu
Functional large-conductance Ca2+- and voltage-activated K+ (BK) channels can be assembled from four 
subunits (Slo1) alone, or together with four auxiliary ß1 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 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 ß1 subunit increased the apparent Ca2+ sensitivity of Slo1 channels, independently of whether the 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, ß1 subunits no longer increased Ca2+ sensitivity when Slo1 tails were replaced by Slo3 tails. The ß1 subunits were still functionally coupled to channels with Slo3 tails, as DHS-I and 17 ß-estradiol activated these channels in the presence of ß1 subunits, but not in their absence. These findings indicate that the increase in apparent Ca2+ sensitivity induced by the ß1 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 ß1 subunit also induced a decrease in voltage sensitivity that occurred with either Slo1 or Slo3 tails. In contrast, the ß1 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 ß1 subunit may be different.
Key Words: Ca2+-activated K+ channel • RCK domain • DHS-I • estrogen • Slo3
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  G. Liu, S. I. Zakharov, L. Yang, R. S. Wu, S.-X. Deng, D. W. Landry, A. Karlin, and S. O. Marx Locations of the {beta}1 transmembrane helices in the BK potassium channel PNAS, August 5, 2008; 105(31): 10727 - 10732. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Yang, G. Zhang, J. Shi, U. S. Lee, K. Delaloye, and J. Cui Subunit-Specific Effect of the Voltage Sensor Domain on Ca2+ Sensitivity of BK Channels Biophys. J., June 15, 2008; 94(12): 4678 - 4687. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Lv, M. Chen, G. Gan, L. Wang, T. Xu, and J. Ding Four-turn {alpha}-Helical Segment Prevents Surface Expression of the Auxiliary h{beta}2 Subunit of BK-type Channel J. Biol. Chem., February 1, 2008; 283(5): 2709 - 2715. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Wang and R. Brenner An S6 Mutation in BK Channels Reveals {beta}1 Subunit Effects on Intrinsic and Voltage-dependent Gating J. Gen. Physiol., December 1, 2006; 128(6): 731 - 744. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Qian, X. Niu, and K. L. Magleby Intra- and Intersubunit Cooperativity in Activation of BK Channels by Ca2+ J. Gen. Physiol., October 1, 2006; 128(4): 389 - 404. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Zhang, X. Zeng, and C. J. Lingle Slo3 K+ Channels: Voltage and pH Dependence of Macroscopic Currents J. Gen. Physiol., August 28, 2006; 128(3): 317 - 336. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. A. Fodor and R. W. Aldrich Statistical Limits to the Identification of Ion Channel Domains by Sequence Similarity J. Gen. Physiol., May 30, 2006; 127(6): 755 - 766. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. S. Ha, H.-H. Lim, G. E. Lee, Y.-C. Kim, and C.-S. Park Electrophysiological Characterization of Benzofuroindole-Induced Potentiation of Large-Conductance Ca2+-Activated K+ Channels Mol. Pharmacol., March 1, 2006; 69(3): 1007 - 1014. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Orio, Y. Torres, P. Rojas, I. Carvacho, M. L. Garcia, L. Toro, M. A. Valverde, and R. Latorre Structural Determinants for Functional Coupling Between the {beta} and {alpha} Subunits in the Ca2+-activated K+ (BK) Channel J. Gen. Physiol., January 30, 2006; 127(2): 191 - 204. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Bao and D. H. Cox Gating and Ionic Currents Reveal How the BKCa Channel's Ca2+ Sensitivity Is Enhanced by its {beta}1 Subunit J. Gen. Physiol., September 26, 2005; 126(4): 393 - 412. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Orio and R. Latorre Differential Effects of {beta}1 and {beta}2 Subunits on BK Channel Activity J. Gen. Physiol., March 28, 2005; 125(4): 395 - 411. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Zhang and F. T. Horrigan Cysteine Modification Alters Voltage- and Ca2+-dependent Gating of Large Conductance (BK) Potassium Channels J. Gen. Physiol., January 31, 2005; 125(2): 213 - 236. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. S. Ha, M.-S. Heo, and C.-S. Park Functional Effects of Auxiliary {beta}4-Subunit on Rat Large-Conductance Ca2+-Activated K+ Channel Biophys. J., May 1, 2004; 86(5): 2871 - 2882. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
X. Qian and K. L. Magleby {beta}1 subunits facilitate gating of BK channels by acting through the Ca2+, but not the Mg2+, activating mechanisms PNAS, August 19, 2003; 100(17): 10061 - 10066. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. I. Brelidze, X. Niu, and K. L. Magleby A ring of eight conserved negatively charged amino acids doubles the conductance of BK channels and prevents inward rectification PNAS, July 22, 2003; 100(15): 9017 - 9022. [Abstract] [Full Text] [PDF]
|
|
|
|
