Cytoplasmic gatekeepers of K+-channel flux: a structural perspective

Roosild, Tarmo P.; Lê, Khanh-Tuoc; Choe, Senyon

doi:10.1016/j.tibs.2003.11.008

Cited by 49 publications

(39 citation statements)

References 49 publications

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“…Based on our results showing that the CBS domains of ClC-1 mediate ATP modulation of common gating, we propose that these domains can be thought of as channel regulatory domains sensitive to intracellular ligands, analogous to the variety of cytoplasmic regulatory domains associated with K ϩ channels (55). ClC proteins comprise a large family of Cl Ϫ -selective ion channels and transporters (56) that are widespread in prokaryotic and eukaryotic cells and are involved in a diverse range of physiological functions (8), but CBS domains are conserved in most ClC proteins (Fig.…”

Section: Discussionmentioning

confidence: 97%

Cytoplasmic ATP-sensing Domains Regulate Gating of Skeletal Muscle ClC-1 Chloride Channels

Bennetts

Rychkov

et al. 2005

Journal of Biological Chemistry

113

162

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ClC proteins are a family of chloride channels and transporters that are found in a wide variety of prokaryotic and eukaryotic cell types. The mammalian voltage-gated chloride channel ClC-1 is important for controlling the electrical excitability of skeletal muscle. Reduced excitability of muscle cells during metabolic stress can protect cells from metabolic exhaustion and is thought to be a major factor in fatigue. Here we identify a novel mechanism linking excitability to metabolic state by showing that ClC-1 channels are modulated by ATP. The high concentration of ATP in resting muscle effectively inhibits ClC-1 activity by shifting the voltage gating to more positive potentials. ADP and AMP had similar effects to ATP, but IMP had no effect, indicating that the inhibition of ClC-1 would only be relieved under anaerobic conditions such as intense muscle activity or ischemia, when depleted ATP accumulates as IMP. The resulting increase in ClC-1 activity under these conditions would reduce muscle excitability, thus contributing to fatigue. We show further that the modulation by ATP is mediated by cystathionine ␤-synthase-related domains in the cytoplasmic C terminus of ClC-1. This defines a function for these domains as gating-modulatory domains sensitive to intracellular ligands, such as nucleotides, a function that is likely to be conserved in other ClC proteins.Skeletal muscle has a high and variable demand for energy, in the form of ATP, and has elaborate systems to maintain the ATP supply. During intense exercise, however, ATP supply may not keep up with demand, and ATP concentration can decrease rapidly. In fast twitch fibers ATP can drop to below 25% of resting concentration within 25 s (1), a rate of ATP consumption that, if it continued, would deplete all ATP within a further 10 s. As the majority of ATP is consumed by the sarcoplasmic reticulum (SR) 5 Ca 2ϩ -ATPase pumping Ca 2ϩ back into the SR after each Ca 2ϩ -activated contraction (2), complete ATP depletion would lead to a rise in cytoplasmic calcium, rigor, and calcium-dependent damage (3, 4). This does not normally occur because force generation and ATP consumption decrease during exercise, compromising short term function but protecting cells from complete metabolic exhaustion. This process is well known as fatigue, but the factors contributing to fatigue remain controversial. A direct reduction in force generation by the contractile apparatus is thought to be a factor early in fatigue (3, 5), but a significant reduction in ATP consumption only occurs with a reduction in SR Ca 2ϩ release (and consequent reuptake) that occurs late in fatigue, correlating with ATP depletion (3). Indeed, ATP depletion and the concomitant increase in cytoplasmic Mg 2ϩ

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Section: Discussionmentioning

confidence: 97%

Cytoplasmic ATP-sensing Domains Regulate Gating of Skeletal Muscle ClC-1 Chloride Channels

Bennetts

Rychkov

et al. 2005

Journal of Biological Chemistry

113

162

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“…Like voltagegated K + channels (Roosild et al, 2004), inwardly rectifying K + channels (Bichet et al, 2003), cyclic nucleotide-gated (CNG) channels (Kaupp and Seifert, 2002) or hyperpolarization-activated and cyclic nucleotide-regulated (HCN) channels (Zagotta et al, 2003;Robinson and Siegelbaum, 2003), TRP channel subunits presumably assemble into homo-or heterotetrameric channel complexes. The subunit composition may influence the biophysical and regulatory properties of the resulting channel complex.…”

Section: Introductionmentioning

confidence: 99%

Homo- and heteromeric assembly of TRPV channel subunits

Hellwig

Albrecht

Harteneck

et al. 2005

Journal of Cell Science

267

247

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The vanilloid receptor-related TRP channels (TRPV1-6) mediate thermosensation, pain perception and epithelial Ca2+ entry. As the specificity of TRPV channel heteromerization and determinants governing the assembly of TRPV subunits were largely elusive, we investigated the TRPV homo- and heteromultimerization. To analyze the assembly of TRPV subunits in living cells, we generated fluorescent fusion proteins or FLAG-tagged TRPV channel subunits. The interaction between TRPV subunits was assessed by analysis of the subcellular colocalization, fluorescence resonance energy transfer and coimmunoprecipitation. Our results demonstrate that TRPV channel subunits do not combine arbitrarily. With the exception of TRPV5 and TRPV6, TRPV channel subunits preferentially assemble into homomeric complexes. Truncation of TRPV1, expression of cytosolic termini of TRPV1 or TRPV4 and construction of chimeric TRPV channel subunits revealed that the specificity and the affinity of the subunit interaction is synergistically provided by interaction modules located in the transmembrane domains and in the cytosolic termini. The relative contribution of intramolecularly linked interaction modules presumably controls the overall affinity and the specificity of TRPV channel assembly.

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“…However, the tetrameric nature of the BK Ca channel suggested the presence of a second RCK domain in the cytosolic domain of the channel for assembly of an octameric gating ring (24,37,38). In this study, we have placed the second RCK domain (RCK2) ϳ100 residues downstream of RCK1 and demonstrated the functional importance of this region.…”

Section: Discussionmentioning

confidence: 99%

“…Mutational Analysis of a Putative Salt Bridge and the Hydrophobic Interface in RCK2-RCK domains contain a structurally important salt bridge in the N-lobe Rossmann fold (24,25,37). In a previous study, mutation of the residues forming the salt bridge in RCK1 decreased the calcium sensitivity of the human Slo channel (25).…”

Section: Bankmentioning

confidence: 94%

“…In the gating ring of the MthK channel, four RCK domains are provided by the four channel subunits. The other four intracellular domains are produced as a result of translation start at downstream initiation sites.Based on the octameric nature of the gating ring, two RCK domains have been proposed to lie in tandem within the long cytoplasmic region of the mammalian BK Ca channel (24,37,38), and an RCK-like domain located at the proximal C terminus of the Slo protein has been characterized in detail using mutational analysis. This domain (RCK1) contains divalent cation binding sites, including the low-affinity site for Ca 2ϩ (27)(28)(29).…”

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confidence: 99%

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Hydrophobic Interface between Two Regulators of K+ Conductance Domains Critical for Calcium-dependent Activation of Large Conductance Ca2+-activated K+ Channels

Kim

Lim

Rho

et al. 2006

Journal of Biological Chemistry

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It has been suggested that the large conductance Ca 2؉ -activated K ؉ channel contains one or more domains known as regulators of K ؉ conductance (RCK) in its cytosolic C terminus. Here, we show that the second RCK domain (RCK2) is functionally important and that it forms a heterodimer with RCK1 via a hydrophobic interface. Mutant channels lacking RCK2 are nonfunctional despite their tetramerization and surface expression. The hydrophobic residues that are expected to form an interface between RCK1 and RCK2, based on the crystal structure of the bacterial MthK channel, are well conserved, and the interactions of these residues were confirmed by mutant cycle analysis. The hydrophobic interaction appears to be critical for the Ca 2؉ -dependent gating of the large conductance Ca 2؉ -activated K ؉ channel.Large conductance calcium-activated potassium (BK Ca ) 2 channels play a key role in modulating a number of important physiological processes, such as neuronal excitability, frequency tuning of hair cells, smooth muscle contraction, and immunity (1-9). BK Ca channels are activated by membrane depolarization and an increase in intracellular calcium (10 -13). Thus, BK Ca channels are considered to be molecular integrators of biochemical and electrical signals. Membrane depolarization and calcium binding activate BK Ca channels independently via separate regions of the ␣ subunit of the channel (Slo). The transmembrane segments of the Slo channel, S1-S6, are structurally similar to those of voltage-gated potassium channels, and as in these channels, charged residues in the Slo S1-S4 segments are thought to be involved in the voltage-dependent gating of the channel (14 -20). It is generally accepted that the bulkycytoplasmicCterminusofSloisresponsibleforthecalciumdependent activation of the channel (21-23).The cytoplasmic C terminus of Slo has been proposed to contain more than two Ca 2ϩ -sensing sites, a high affinity site called the Ca 2ϩ bowl, a low affinity site, and additional high affinity sites within a structural module known as the regulator of K ϩ conductance (RCK) domain (22, 24 -29). The Ca 2ϩ bowl is composed of a series of Asp residues and binds Ca 2ϩ with micromolar affinity. Mutations here have been shown to cause positive shifts in the conductance-voltage (G-V) relationship at constant [Ca 2ϩ ], which are similar to those observed with the wild-type channel when [Ca 2ϩ ] is lowered (22,23,26,30,31). The RCK domain is found primarily in prokaryotic ligandgated K ϩ channels and in some bacterial K ϩ uptake and efflux systems, in which it is also called the K ϩ transport nucleotidebinding (KTN) domain (25,(32)(33)(34). Crystal structures of RCK domains have been determined from Ca 2ϩ -activated K ϩ channels in Escherichia coli and Methanobacterium thermoautotrophicum (24,25,35,36). The structure of the tetrameric MthK channel shows that an octameric complex could be formed by intermolecular interactions on fixed and flexible interfaces between a tetramer of dimeric RCK domains. This complex, called the...

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Cytoplasmic gatekeepers of K+-channel flux: a structural perspective

Cited by 49 publications

References 49 publications

Cytoplasmic ATP-sensing Domains Regulate Gating of Skeletal Muscle ClC-1 Chloride Channels

Cytoplasmic ATP-sensing Domains Regulate Gating of Skeletal Muscle ClC-1 Chloride Channels

Homo- and heteromeric assembly of TRPV channel subunits

Hydrophobic Interface between Two Regulators of K+ Conductance Domains Critical for Calcium-dependent Activation of Large Conductance Ca2+-activated K+ Channels

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