The Journal of General Physiology
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Published online 15 August 2005 doi:10.1085/jgp.200509321
The Rockefeller University Press, 0022-1295 $8.00
JGP, Volume 126, Number 3, 227-241
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ARTICLE

 The NH2 Terminus of RCK1 Domain Regulates Ca2+-dependent BKCa Channel Gating

Gayathri Krishnamoorthy1, Jingyi Shi2,3, David Sept2,4, and Jianmin Cui2,3

1 Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106
2 Department of Biomedical Engineering, Washington University, St. Louis, MO 63130
3 Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130
4 Center for Computational Biology, Washington University, St. Louis, MO 63130

Correspondence to Jianmin Cui: jcui{at}biomed.wustl.edu

Large conductance, voltage- and Ca2+-activated K+ (BKCa) channels regulate blood vessel tone, synaptic transmission, and hearing owing to dual activation by membrane depolarization and intracellular Ca2+. Similar to an archeon Ca2+-activated K+ channel, MthK, each of four {alpha} subunits of BKCa may contain two cytosolic RCK domains and eight of which may form a gating ring. The structure of the MthK channel suggests that the RCK domains reorient with one another upon Ca2+ binding to change the gating ring conformation and open the activation gate. Here we report that the conformational changes of the NH2 terminus of RCK1 (AC region) modulate BKCa gating. Such modulation depends on Ca2+ occupancy and activation states, but is not directly related to the Ca2+ binding sites. These results demonstrate that AC region is important in the allosteric coupling between Ca2+ binding and channel opening. Thus, the conformational changes of the AC region within each RCK domain is likely to be an important step in addition to the reorientation of RCK domains leading to the opening of the BKCa activation gate. Our observations are consistent with a mechanism for Ca2+-dependent activation of BKCa channels such that the AC region inhibits channel activation when the channel is at the closed state in the absence of Ca2+; Ca2+ binding and depolarization relieve this inhibition.

Abbreviations used in this paper: MWC, Monod-Wyman-Changeux; WT, wild-type.


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