Tetraethylammonium block of Slowpoke calcium-activated potassium channels expressed in Xenopus oocytes: Evidence for tetrameric channel formation

Shen, Ke Zhong; Lagrutta, Armando; Davies, Noel W.; Standen, N B; Adelman, John P.; North, R A

doi:10.1007/bf00388308

Cited by 174 publications

(144 citation statements)

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“…Y294V abolishes BK channel sensitivity to extracellular tetraethylammonium (TEA) (21). In the presence of extracellular TEA, the conductance of the resulting channel is determined by the number of Y294V subunits in the channel, thereby defining the stoichiometry of each channel from its …”

Section: Significancementioning

confidence: 99%

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Zhou

Xia

Lingle

2015

Proc. Natl. Acad. Sci. U.S.A.

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To probe structure and gating-associated conformational changes in BK-type potassium (BK) channels, we examined consequences of Cd 2+ coordination with cysteines introduced at two positions in the BK inner pore. At V319C, the equivalent of valine in the conserved Kv proline-valine-proline (PVP) motif, Cd 2+ forms intrasubunit coordination with a native glutamate E321, which would place the side chains of V319C and E321 much closer together than observed in voltage-dependent K + (Kv) channel structures, requiring that the proline between V319C and E321 introduces a kink in the BK S6 inner helix sharper than that observed in Kv channel structures. At inner pore position A316C, Cd 2+ binds with modest state dependence, suggesting the absence of an ion permeation gate at the cytosolic side of BK channel. These results highlight fundamental structural differences between BK and Kv channels in their inner pore region, which likely underlie differences in voltagedependent gating between these channels.H ow transmembrane potential influences the opening and closing of ion channels, a process known as gating, is central to understanding how cellular excitability is regulated (1). For voltage-dependent K + (Kv) channels, functional (2-4) and crystallographic (5, 6) studies have led to a compelling model of gating. In this model there are two key elements, both of which arise from properties of the cytosolic end of Kv channels: a cytosolic ion permeation gate formed by an interlaced arrangement of S6 inner helices termed the bundle crossing (2, 3), and a kink produced by the conserved proline-valine-proline (PVP) motif (Fig. 1A, boxed residues) to allow the C terminus of Kv S6 to form extensive contact with the S4-S5 linker (5, 6). Thus, the outward movement of the voltage sensors (VSDs) induced by transmembrane depolarization is thought to be transmitted to S6 through the S4-S5 linker to open the cytosolic ion permeation gate (6-8), and this enables access of cytosolic K + ions to the Kv inner pore region.Although this model is generally accepted for Kv channel gating, it is not clear to what extent it applies to other K + channels. For example, the large conductance, Ca 2+ -activated K + (BK or Slo1) channel shares with Kv channels a similar set of four VSDs attached to a central pore and gate domain (PGD), such that both channels are voltage dependent (9). However, unlike that of Kv channels, the inner pore of a closed BK channels is accessible to large molecules such as quaternary ammonium (QA) blockers (10, 11) and methanethiosulfonate ethyltrimethylammonium (MTSET) (12), indicating that the cytosolic end of a closed BK channel cannot completely occlude K + flow; this indicates that a gate extracellular to that proposed for Kv channels is required to securely prevent K + flow in a closed BK channel. As a corollary, the underlying structural and conformational details required to couple VSD activation to channel opening may differ between BK and Kv channels.To provide new insight into differences between BK and Kv in t...

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Section: Significancementioning

confidence: 99%

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Zhou

Xia

Lingle

2015

Proc. Natl. Acad. Sci. U.S.A.

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“…In the case of Kv channels, the channelforming protein possesses six transmembrane domains (S1-S6) containing the pore-forming domain S5-P-S6 and an S4 voltage-sensing element. Like Kv channels, the BK channel is a tetramer (Shen et al, 1994); unlike Kv channels, however, the BK channel protein consists of seven transmembrane domains (S0-S6) that lead to an exoplasmic N-terminus (Fig. 1;Meera et al, 1997;Wallner et al, 1996;Toro et al, 1998).…”

Section: Sensing Elementsmentioning

confidence: 99%

“…The Ca 2+ bowl of mSlo1 was disrupted by deleting aspartates 965 and 966, and the number of bowls per channel determined by mixing TEA-insensitive subunits with bowl-disrupted subunits. Stoichiometry is obtained from the singlechannel current amplitudes (see also Shen et al, 1994).…”

Section: Explaining Bk Channel Activity Using Allosteric Modelsmentioning

confidence: 99%

Large conductance Ca2+-activated K+ (BK) channel: Activation by Ca2+ and voltage

2006

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Large conductance Ca 2+ -activated K + (BK) channels belong to the S4 superfamily of K + channels that include voltage-dependent K + (Kv) channels characterized by having six (S1-S6) transmembrane domains and a positively charged S4 domain. As Kv channels, BK channels contain a S4 domain, but they have an extra (S0) transmembrane domain that leads to an external NH 2 -terminus. The BK channel is activated by internal Ca 2+ , and using chimeric channels and mutagenesis, three distinct Ca 2+ -dependent regulatory mechanisms with different divalent cation selectivity have been identified in its large COOH-terminus. Two of these putative Ca 2+ -binding domains activate the BK channel when cytoplasmic Ca 2+ reaches micromolar concentrations, and a low Ca 2+ affinity mechanism may be involved in the physiological regulation by Mg 2+ . The presence in the BK channel of multiple Ca 2+ -binding sites explains the huge Ca 2+ concentration range (0.1 μM-100 μM) in which the divalent cation influences channel gating. BK channels are also voltage-dependent, and all the experimental evidence points toward the S4 domain as the domain in charge of sensing the voltage. Calcium can open BK channels when all the voltage sensors are in their resting configuration, and voltage is able to activate channels in the complete absence of Ca 2+ . Therefore, Ca 2+ and voltage act independently to enhance channel opening, and this behavior can be explained using a two-tiered allosteric gating mechanism.

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“…As such, they are potent regulators of diverse cellular processes, including smooth muscle tone, neuronal excitability, and neurotransmitter release (8). Four pore-forming α subunits (10), encoded by KCNMA1 (hSlo1) in humans (11), are required to assemble into a functional channel. Each α subunit possesses an extracellular N terminus (12), seven transmembrane segments (S0-S6), and a large intracellular C-terminal region organized into domains RCK1 and RCK2 (Regulator of Conductance for K + , Fig.…”

mentioning

confidence: 99%

Operation of the voltage sensor of a human voltage- and Ca ²⁺ -activated K ⁺ channel

Pantazis

Gudzenko²,

Savalli³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Voltage sensor domains (VSDs) are structurally and functionally conserved protein modules that consist of four transmembrane segments (S1-S4) and confer voltage sensitivity to many ion channels. Depolarization is sensed by VSD-charged residues residing in the membrane field, inducing VSD activation that facilitates channel gating. S4 is typically thought to be the principal functional component of the VSD because it carries, in most channels, a large portion of the VSD gating charge. The VSDs of large-conductance, voltage-and Ca 2+ -activated K + channels are peculiar in that more gating charge is carried by transmembrane segments other than S4. Considering its "decentralized" distribution of voltage-sensing residues, we probed the BK Ca VSD for evidence of cooperativity between charge-carrying segments S2 and S4. We achieved this by optically tracking their activation by using voltage clamp fluorometry, in channels with intact voltage sensors and charge-neutralized mutants. The results from these experiments indicate that S2 and S4 possess distinct voltage dependence, but functionally interact, such that the effective valence of one segment is affected by charge neutralization in the other. Statisticalmechanical modeling of the experimental findings using allosteric interactions demonstrates two mechanisms (mechanical coupling and dynamic focusing of the membrane electric field) that are compatible with the observed cross-segment effects of charge neutralization. increase (1-9) results in an exceptionally high conductance for K + . As such, they are potent regulators of diverse cellular processes, including smooth muscle tone, neuronal excitability, and neurotransmitter release (8). Four pore-forming α subunits (10), encoded by KCNMA1 (hSlo1) in humans (11), are required to assemble into a functional channel. Each α subunit possesses an extracellular N terminus (12), seven transmembrane segments (S0-S6), and a large intracellular C-terminal region organized into domains RCK1 and RCK2 (Regulator of Conductance for K + , Fig. 1A) that confer sensitivity to Ca 2+ and other intracellular ligands (8,9,(13)(14)(15)(16)(17)(18)(19)(20). Segments S1-S6 are structurally and functionally homologous to those of other voltage-gated ion channels (21), with S1-S4 comprising the VSD, whereas S5 and S6 contribute to the K + -selective pore.Our understanding of VSD structure and function has been achieved thus far through analysis of crystal structures (22-24) as well as accessibility, electrophysiological, and optical investigations in functional proteins (reviewed in ref. 25). VSDs possess a high density of charged residues (Fig. 1C). Upon membrane potential depolarization, a subset of these residues may traverse the field partially or entirely, initiating conformational rearrangements that propagate to the channel gate, facilitating ionic conductance (26-28). S4 is thought to be the principal voltagesensing segment because, in most VSD-gated channels, it contributes the greatest portion of gating charge movement (29-31). S2 ...

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Tetraethylammonium block of Slowpoke calcium-activated potassium channels expressed in Xenopus oocytes: Evidence for tetrameric channel formation

Cited by 174 publications

References 19 publications

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Large conductance Ca2+-activated K+ (BK) channel: Activation by Ca2+ and voltage

Operation of the voltage sensor of a human voltage- and Ca ²⁺ -activated K ⁺ channel

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Tetraethylammonium block of Slowpoke calcium-activated potassium channels expressed in Xenopus oocytes: Evidence for tetrameric channel formation

Cited by 174 publications

References 19 publications

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

Large conductance Ca2+-activated K+ (BK) channel: Activation by Ca2+ and voltage

Operation of the voltage sensor of a human voltage- and Ca 2+ -activated K + channel

Contact Info

Product

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Operation of the voltage sensor of a human voltage- and Ca ²⁺ -activated K ⁺ channel