How Does the W434F Mutation Block Current in Shaker Potassium Channels?

Abstract

The mutation W434F produces an apparently complete block of potassium current in Shaker channels expressed in Xenopus oocytes. Tandem tetrameric constructs containing one or two subunits with this mutation showed rapid inactivation, although the NH2-terminal inactivation domain was absent from these constructs. The inactivation showed a selective dependence on external cations and was slowed by external TEA; these properties are characteristic of C-type inactivation. Inactivation was, however, incompletely relieved by hyperpolarization, suggesting the presence of a voltage-independent component. The hybrid channels had near-normal conductance and ion selectivity. Single-channel recordings from patches containing many W434F channels showed occasional channel openings, consistent with open probabilities of 10−5 or less. We conclude that the W434F mutation produces a channel that is predominantly found in an inactivated state.

Closed state-coupled C-type inactivation in BK channels

“…From voltage-clamp fluorometry data (41), it was suggested that the inactivation of Shaker channels comprises an initial closure of the inactivation gate, referred as "P-type" inactivation, which was related to an onset of macroscopic inactivation and exhibited no gating charge immobilization (41). This P-type inactivation is similar to what was observed in a constitutively inactivated W434F Shaker mutant, which still has a normal C ↔ O transition, as indicated by the largely intact voltage-dependent gating charge movements (28). It is plausible that the BK channel's normal closure/deactivation may resemble P-type inactivation.…”

“…In Shaker channels, the W434F mutation can lead to constitutive C-type inactivation (28). In BK channels, the equivalent position is Y279.…”

“…It is reasonable to assume that the BK channel pore, particularly within and near the selectivity filter region, may share a similar structure with other K + channels and thus is essentially capable of undergoing C-type inactivation. It was well established that C-type inactivation in Shaker channels can be hastened drastically by single-point mutations at position Thr449 or Trp434 or by a decrease in external K + concentration (25)(26)(27)(28)(29). To explore the hypothesis that the BK channel's activation gate may exist near or at the selectivity filter, we tested ways to induce Significance Ion channels regulate ion flow by opening and closing their pore gates.…”

Concerted All-or-none Subunit Interactions Mediate Slow Deactivation of Human ether-à-go-go-related Gene K+ Channels

“…C-type inactivation of K V 1 channels is mediated by a subtle structural rearrangement of the selectivity filter (52)(53)(54). Similar to slow deactivation in WT hERG1a, C-type inactivation of K V 1 channels involves highly cooperative subunit interactions (49,55,56). N-type inactivation is mediated by blocking the channel pore by an N-terminal "ball" domain (57,58) or by the N terminus of an accessory ␤-subunit (59,60).…”

Moving gating charges through the gating pore in a Kv channel voltage sensor

“…Gating currents produced during the resting-to-active (activation) and active-to-resting (deactivation) transitions were recorded in the 99 functional mutants by blocking K + conduction using the mutation W434F, which favors a nonconducting (inactivated) state of the channel's pore (50)(51)(52). Activation gating currents were elicited by using depolarizing pulses (Fig.…”