Defining the BK channel domains required for beta1-subunit modulation.
In a wide variety of cell types, including neurons and smooth muscle cells, activation of the large-conductance voltage- and Ca(2+)-activated K(+) (BK) channels causes transient membrane hyperpolarization, thereby regulating cellular excitability. Similar to other voltage-gated ion channels, BK channels, a tetramer of alpha-subunits, associate with auxiliary beta-subunits in a tissue-specific manner, modifying the channel's gating properties. The BK beta1-subunit, which is expressed in smooth muscle, increases the apparent Ca(2+) sensitivity (marked by a hyperpolarizing shift in the conductance-voltage relationship at a given Ca(2+) concentration), slows macroscopic activation and deactivation, and is required for channel activation by 17beta-estradiol. The beta1-subunit is essential for normal regulation of vascular smooth muscle contractility and blood pressure. Little is known, however, about the molecular mechanisms of beta1-subunit modulation of alpha-subunits. Here we show that the beta1-subunit's modulation of the Ca(2+) and 17beta-estradiol sensitivities can be dissociated from its effects on gating kinetics by truncation of the alpha-subunit's extracellular N-terminal residues. The BK alpha-subunit N terminus interacts uniquely with the beta1-subunit: beta2 regulation of the alpha-subunit is unaltered by truncation of the N terminus. Although the functional interaction of alpha and beta1 requires the N-terminal tail of alpha, the physical association requires the S1, S2, and S3 transmembrane helices of alpha.
Division of Cardiology, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
John P
JP
Morrow
Sergey I
SI
Zakharov
Guoxia
G
Liu
Lin
L
Yang
Andrea J
AJ
Sok
Steven O
SO
Marx
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004594:Electrophysiology; D004958:Estradiol / Q000494:pharmacology; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*
D024681:Potassium Channels, Calcium-Activated; D021122:Protein Subunits; D004958:Estradiol