Contribution of the Selectivity Filter to Inactivation in Potassium Channels

Kiss, László; LoTurco, Joseph J.; Korn, Stephen J.

doi:10.1016/s0006-3495(99)77194-8

Cited by 165 publications

(196 citation statements)

References 27 publications

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“…There is evidence that the filter region plays an important role in the gating of the closely related TRPV1 channel (26,37), and filter region gating underlies C-type inactivation in other cation channels (38). If such a mechanism is at play here, then it is tempting to speculate that voltage is not directly controlling gating but instead the direction of the driving force (i.e.…”

Section: Discussionmentioning

confidence: 98%

Forward Genetic Analysis Reveals Multiple Gating Mechanisms of TRPV4

Loukin

Kung

2010

Journal of Biological Chemistry

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TRPV4 is a polymodal cation channel gain-of-function (GOF) allele which causes skeletal dysplasia in humans. To better understand its gating, we screened for additional GOF alleles based on their ability to block yeast proliferation. Repeatedly, only a limited number of such growth-blocking mutations were isolated. Expressed in oocytes, wild-type channels can be strongly activated by either hypotonicity or exposure to the potent agonist 4␣PDD, although the GOF channels behaved as if they were fully prestimulated as well as lacking a previously uncharacterized voltage-dependent inactivation. Five of six mutations occurred at or near the inner ends of the predicted core helices, giving further direct evidence that this region indeed forms the main intracellular gate in TRP channels. Surprisingly, both wild-type channels as well as these GOF channels maintain strong steady-state outward rectification that is not due to a Ca 2؉ block, as has been proposed elsewhere. We conclude that TRPV4 contains an additional voltage-dependent gating mechanism in series with the main intracellular gate. Transient receptor potential (TRP)2 channels are a functionally and evolutionarily diverse group of cation-selective channels characterized by polymodal gating to chemical, thermal, mechanical as well as other stimuli (1). Predicted transmembrane topology and cryomicroscopic images (2) indicate that TRPs are structurally similar to other cationic channels such as the voltage-gated K ϩ channels (3). Each of the four subunits (4) is modeled to have six transmembrane helices (S1-S6), where S1-S4 forms the peripheral domain and the four S5-S6 domains converge to form the core, with the S6 lining the ion pathway. An ion filter is found in the pathway near the outer half (5). Structural homology to K ϩ channels (3) indicates (6, 7) and direct mutational analysis supports (8) that the cytoplasmic ends of the four S6 conditionally converge to occlude the pathway, creating an intracellular gate.TRPV4, of the vanilloid class of TRP channels, originally drew attention and was isolated based on its ability to respond to hypotonic stress (9, 10). It was subsequently found to also be activated by heat (11), the arachidonic acid (AA) metabolite 5Ј,6Ј-epoxyeicosatrienoic acid (5Ј,6Ј-EET) (12) as well as other compounds (13,14), but the most potent activator was found to be an exogenous agonist, 4␣-phorbol 12,13-didecanoate (4␣PDD) (15). 4␣PDD and hypotonicity were found to activate TRPV4 through distinct pathways (16). In cultured kidney cells, hypotonicity is thought to activate TRPV4 through the production of 5Ј,6Ј-EET, possibly by activating phospholipase A2 (16). There must be other mechanisms by which TRPV4 is activated by hypotonicity, since it maintains robust hypotonic activation when expressed in yeast, which is incapable of synthesizing polyunsaturated fatty acids such as AA and its metabolites (17). TRPV4 is expressed in a broad range of tissue types that have varying physiological relevance (18). TRPV4Ϫ/Ϫ knock-out mice are compromised...

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Section: Discussionmentioning

confidence: 98%

Forward Genetic Analysis Reveals Multiple Gating Mechanisms of TRPV4

Loukin

Kung

2010

Journal of Biological Chemistry

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“…Many Kv channels display C-type inactivation, and it has been shown to be a process that involves conformational changes at the level of the selectivity filter (37)(38)(39)(40)(41). At least two mechanisms have been proposed for constriction of the selectivity filter: 1) a reorientation of the VSD (42,43) or 2) a rearrangement in S6 after channel opening that is transmitted to the selectivity filter destabilizing its conducting conformation (41).…”

Section: Electromechanical Coupling Consists Of Multiple S4s5 L -S6 Tmentioning

confidence: 99%

The S4-S5 Linker of KCNQ1 Channels Forms a Structural Scaffold with the S6 Segment Controlling Gate Closure

Labro

Boulet

Choveau

et al. 2011

Journal of Biological Chemistry

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In vivo, KCNQ1 ␣-subunits associate with the ␤-subunit KCNE1 to generate the slowly activating cardiac potassium current (I Ks ). Structurally, they share their topology with other Kv channels and consist out of six transmembrane helices (S1-S6) with the S1-S4 segments forming the voltage-sensing domain (VSD). The opening or closure of the intracellular channel gate, which localizes at the bottom of the S6 segment, is directly controlled by the movement of the VSD via an electromechanical coupling. In other Kv channels, this electromechanical coupling is realized by an interaction between the S4-S5 linker (S4S5 L ) and the C-terminal end of S6 (S6 T ). Previously we reported that substitutions for Leu 353 in S6 T resulted in channels that failed to close completely. Closure could be incomplete because Leu 353 itself is the pore-occluding residue of the channel gate or because of a distorted electromechanical coupling. To resolve this and to address the role of S4S5 L in KCNQ1 channel gating, we performed an alanine/tryptophan substitution scan of S4S5 L . The residues with a "high impact" on channel gating (when mutated) clustered on one side of the S4S5 L ␣-helix. Hence, this side of S4S5 L most likely contributes to the electromechanical coupling and finds its residue counterparts in S6 T . Accordingly, substitutions for Val 254 resulted in channels that were partially constitutively open and the ability to close completely was rescued by combination with substitutions for Leu 353 in S6 T . Double mutant cycle analysis supported this cross-talk indicating that both residues come in close contact and stabilize the closed state of the channel.KCNQ1 (KvLQT1) ␣-subunits tetramerize to create a voltage-gated K ϩ (Kv) channel. Like other Kv channels, each ␣-subunit contains six membrane spanning segments (S1-S6) with a pore loop between the fifth and sixth segment that forms the selectivity filter. The co-assembly with KCNE1 (minK) ␤-subunits generates the channel complex that underlies the native I Ks in the heart (1, 2). A fundamental property of all Kv channels is their ability to detect a change in membrane potential (V m ) and to respond to this change by opening or closing their activation gate that seals off the ion permeation pathway in a closed configuration (3, 4). The channel activation gate is located in the C-terminal end of the S6 segment (S6 T ), 3 whereas the voltage-sensing domain (VSD) is formed by the S1-S4 segments with the charged S4 as the main component (5). Substitution of the S4 charges in KCNQ1 perturbed channel gating (6, 7) and gating currents that originate from the redistribution of these S4 charges have recently been recorded for the KCNQ family of Kv channels (8). These data indicate that as in Shaker-type channels, the S1-S4 segment in KCNQ1 forms the channel VSD that reorients upon a change in membrane potential. This VSD reorientation is then translated into channel gate opening or closure through an electromechanical coupling. This coupling mechanism remains poorly defined but sev...

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“…Conduction of potassium ions through the central pore of tetrameric potassium channels can be switched on and off by gates at either end of the conduction pathway (1). The selectivity filter, located at the extracellular end of the conduction axis (2), is critical not only for the exquisite selectivity for potassium ions (3,4), but also for gating (5)(6)(7)(8)(9). Gating at the selectivity filter is commonly referred to as C-type inactivation.…”

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confidence: 99%