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Structure of the gating ring from the human large-conductance Ca(2+)-gated K(+) channel.

ABSTRACT: Large-conductance Ca(2+)-gated K(+) (BK) channels are essential for many biological processes such as smooth muscle contraction and neurotransmitter release. This group of channels can be activated synergistically by both voltage and intracellular Ca(2+), with the large carboxy-terminal intracellular portion being responsible for Ca(2+) sensing. Here we present the crystal structure of the entire cytoplasmic region of the human BK channel in a Ca(2+)-free state. The structure reveals four intracellular subunits, each comprising two tandem RCK domains, assembled into a gating ring similar to that seen in the MthK channel and probably representing its physiological assembly. Three Ca(2+) binding sites including the Ca(2+) bowl are mapped onto the structure based on mutagenesis data. The Ca(2+) bowl, located within the second RCK domain, forms an EF-hand-like motif and is strategically positioned close to the assembly interface between two subunits. The other two Ca(2+) (or Mg(2+)) binding sites, Asp 367 and Glu 374/Glu 399, are located on the first RCK domain. The Asp 367 site has high Ca(2+) sensitivity and is positioned in the groove between the amino- and carboxy-terminal subdomains of RCK1, whereas the low-affinity Mg(2+)-binding Glu 374/Glu 399 site is positioned on the upper plateau of the gating ring and close to the membrane. Our structure also contains the linker connecting the transmembrane and intracellular domains, allowing us to dock a voltage-gated K(+) channel pore of known structure onto the gating ring with reasonable accuracy and generate a structural model for the full BK channel.

SUBMITTER: Wu Y

PROVIDER: S-EPMC2910425 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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Structure of the gating ring from the human large-conductance Ca(2+)-gated K(+) channel.

Wu Yunkun Y Yang Yi Y Ye Sheng S Jiang Youxing Y

Nature 20100623 7304

Large-conductance Ca(2+)-gated K(+) (BK) channels are essential for many biological processes such as smooth muscle contraction and neurotransmitter release. This group of channels can be activated synergistically by both voltage and intracellular Ca(2+), with the large carboxy-terminal intracellular portion being responsible for Ca(2+) sensing. Here we present the crystal structure of the entire cytoplasmic region of the human BK channel in a Ca(2+)-free state. The structure reveals four intrac ...[more]

PMID: 20574420

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Project description:Cyclic nucleotide-gated (CNG) ion channels are nonselective cation channels, essential for visual and olfactory sensory transduction. Although the channels include voltage-sensor domains (VSDs), their conductance is thought to be independent of the membrane potential, and their gating regulated by cytosolic cyclic nucleotide-binding domains. Mutations in these channels result in severe, degenerative retinal diseases, which remain untreatable. The lack of structural information on CNG channels has prevented mechanistic understanding of disease-causing mutations, precluded structure-based drug design, and hampered in silico investigation of the gating mechanism. To address this, we built a 3D model of the cone tetrameric CNG channel, based on homology to two distinct templates with known structures: the transmembrane (TM) domain of a bacterial channel, and the cyclic nucleotide-binding domain of the mouse HCN2 channel. Since the TM-domain template had low sequence-similarity to the TM domains of the CNG channels, and to reconcile conflicts between the two templates, we developed a novel, hybrid approach, combining homology modeling with evolutionary coupling constraints. Next, we used elastic network analysis of the model structure to investigate global motions of the channel and to elucidate its gating mechanism. We found the following: (i) In the main mode of motion, the TM and cytosolic domains counter-rotated around the membrane normal. We related this motion to gating, a proposition that is supported by previous experimental data, and by comparison to the known gating mechanism of the bacterial KirBac channel. (ii) The VSDs could facilitate gating (supplementing the pore gate), explaining their presence in such 'voltage-insensitive' channels. (iii) Our elastic network model analysis of the CNGA3 channel supports a modular model of allosteric gating, according to which protein domains are quasi-independent: they can move independently, but are coupled to each other allosterically.

Dataset Information

Structure of the gating ring from the human large-conductance Ca(2+)-gated K(+) channel.

Publications

Structure of the gating ring from the human large-conductance Ca(2+)-gated K(+) channel.

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