Modulation of BK channel gating by the ß2 subunit involves both membrane-spanning and cytoplasmic domains of Slo1.
Large-conductance, Ca(2+)- and voltage-sensitive K(+) (BK) channels regulate neuronal functions such as spike frequency adaptation and transmitter release. BK channels are composed of four Slo1 subunits, which contain the voltage-sensing and pore-gate domains in the membrane and Ca(2+) binding sites in the cytoplasmic domain, and accessory β subunits. Four types of BK channel β subunits (β1-β4) show differential tissue distribution and unique functional modulation, resulting in diverse phenotypes of BK channels. Previous studies show that both the β1 and β2 subunits increase Ca(2+) sensitivity, but different mechanisms may underline these modulations. However, the structural domains in Slo1 that are critical for Ca(2+)-dependent activation and targeted by these β subunits are not known. Here, we report that the N termini of both the transmembrane (including S0) and cytoplasmic domains of Slo1 are critical for β2 modulation based on the study of differential effects of the β2 subunit on two orthologs, mouse Slo1 and Drosophila Slo1. The N terminus of the cytoplasmic domain of Slo1, including the AC region (βA-αC) of the RCK1 (regulator of K(+) conductance) domain and the peptide linking it to S6, both of which have been shown previously to mediate the coupling between Ca(2+) binding and channel opening, is specifically required for the β2 but not for the β1 modulation. These results suggest that the β2 subunit modulates the coupling between Ca(2+) binding and channel opening, and, although sharing structural homology, the BK channel β subunits interact with structural domains in the Slo1 subunit differently to enhance channel activity.
Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, Missouri 63130, USA.
Urvi S
US
Lee
Jingyi
J
Shi
Jianmin
J
Cui
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D003593:Cytoplasm / Q000737:chemistry / Q000502:physiology*; D004330:Drosophila; D005260:Female; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits / Q000737:chemistry / Q000502:physiology*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000737:chemistry / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D050506:Mutant Chimeric Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics; D014982:Xenopus laevis
C531905:KCNMB1 protein, human; C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D051038:Large-Conductance Calcium-Activated Potassium Channel beta Subunits; D051036:Large-Conductance Calcium-Activated Potassium Channels; D050506:Mutant Chimeric Proteins