Molecular basis for functional connectivity between the voltage sensor and the selectivity filter gate in Shaker K+ channels

Abstract

In Shaker K+ channels, the S4-S5 linker couples the voltage sensor (VSD) and pore domain (PD). Another coupling mechanism is revealed using two W434F-containing channels: L361R:W434F and L366H:W434F. In L361R:W434F, W434F affects the L361R VSD seen as a shallower charge-voltage (Q-V) curve that crosses the conductance-voltage (G-V) curve. In L366H:W434F, L366H relieves the W434F effect converting a non-conductive channel in a conductive one. We report a chain of residues connecting the VSD (S4) to the selectivity filter (SF) in the PD of an adjacent subunit as the molecular basis for voltage sensor selectivity filter gate (VS-SF) coupling. Single alanine substitutions in this region (L409A, S411A, S412A, or F433A) are enough to disrupt the VS-SF coupling, shown by the absence of Q-V and G-V crossing in L361R:W434F mutant and by the lack of ionic conduction in the L366H:W434F mutant. This residue chain defines a new coupling between the VSD and the PD in voltage-gated channels.

Experimental challenges in ion channel research: uncovering basic principles of permeation and gating in potassium channels

“…However, this energy should be accounted for both canonical and the noncanonical coupling process. Nevertheless, we found that the noncanonical coupling was efficient in transferring information to both the activation gate and to the selectivity filter gate [36]. The modulation of the activation gate by means of the noncanonical coupling mechanism is undoubtedly more relevant when some mutations are present in the VSD and in the PD [45].…”

“…Recently, structural biology studies combined with molecular dynamics and functional assays have revealed other coupling mechanisms in VGKC that are called noncanonical coupling [36][37][38][39]. These noncanonical mechanisms do not depend on the S4-S5 linker-based canonical coupling mentioned above.…”

“…Recently, we uncovered another case where the noncanonical mechanism is playing a role. A single mutation in the S4 VSD (L366H) that relieves the inactivation induced by W434F [36]. We then designed a set of experiments intended to probe whether the hypothesized chain is the molecular basis for the noncanonical coupling mechanism in Shaker.…”

“…Whenever we interrupted the chain (shown in Figure 3), we produced conspicuous changes on how the VSD couples to the PD. In the case of the L361R with W434F mutations, any interruption of the chain eliminated the Q-V and G-V crossing; and in the case of the L366H with W434F mutations, any interruption of the chain restored the inactivation of the W434F mutation [36]. Altogether, these observations (1) suggest that the chained amino acid residues are functionally coupled among them and (2) demonstrate that the proposed residues are indeed the molecular basis for the noncanonical coupling mechanism.…”

Cryo-EM structure of the human Kv3.1 channel reveals gating control by the cytoplasmic T1 domain

“…These ndings are ground-breaking in light of the current model of electromechanical coupling in Kv channels, where the transmembrane region is thought to be primarily responsible for the transmission of signal between the VSD and the pore: the S4/S5 linker is considered an important coupling device transmitting conformational changes in the S4 voltage sensors to the pore domain via interactions with the S6 C-termini [45,46] and direct interactions between S4 and S5 have been proposed as a noncanonical coupling pathway [47][48][49]. Due to the remarkable degree of sequence conservation of the S4/S5 linker in Kv3 channels across species, this region was previously suggested to be linked to the specialized Kv3 properties and driving their evolution in vertebrates [2].…”