Metal Bridge in S4 Segment Supports Helix Transition in Shaker Channel

Abstract

Voltage-gated ion channels play important roles in physiological processes, especially in excitable cells, in which they shape the action potential. In S4-based voltage sensors voltage-gated channels, a common feature is shared; the transmembrane segment 4 (S4) contains positively charged residues intercalated by hydrophobic residues. Although several advances have been made in understating how S4 moves through a hydrophobic plug upon voltage changes, the possible helix transition from a-to 3 10-helix in S4 during the activation process is still unresolved. Here, we have mutated several hydrophobic residues from I360 to F370 in the S4 segment into histidine, in i, i þ 3 and i, i þ 6 or i, i þ 4 and i, i þ 7 pairs, to favor 3 10-or a-helical conformations, respectively. We have taken advantage of the ability of His to coordinate Zn 2þ to promote metal ion bridges, and we have found that the histidine introduced at position 366 (L366H) can interact with the introduced histidine at position 370 (stabilizing that portion of the S4 segment in a-helical conformation). In the presence of 20 mM of Zn 2þ , the activation currents of L366H:F370H channels were slowed down by a factor of 3.5, and the voltage dependence is shifted by 10 mV toward depolarized potentials with no change on the deactivation time constant. Our data supports that by stabilizing a region of the S4 segment in a-helical conformation, a closed (resting or intermediate) state is stabilized rather than destabilizing the open (active) state. Taken together, our data indicates that S4 undergoes a-helical conformation to a short-lived different secondary structure transiently before reaching the active state in the activation process.

Mechanism of Voltage Gating in the Voltage-Sensing Phosphatase Ci-VSP

“…Methanesulfonic acid was used for pH adjustment. When needed, Cd 2+ was diluted in the external solution without EDTA at designed concentration from a 100 mM CdCl 2 stock solution 67 . 1~2 mM DTT was freshly added to the external solution to chelate/washout the Cd 2+ ions.…”

Roles for Countercharge in the Voltage Sensor Domain of Ion Channels

“…A consensus model of the resting state was then proposed (Vargas et al, 2012). While simulations have suggested that the S4 segment adopts a 3 10 helical secondary structure to favor the resting state and align S4 arginine side chains with those of negative countercharges (Villalba-Galea et al, 2008;Khalili-Araghi et al, 2010;Schow et al, 2010;Schwaiger et al, 2011), the functional contribution of 3 10 helical structure to VGIC gating remains to be clearly elucidated (Kubota et al, 2014;Bassetto et al, 2019).…”

Non-canonical helical transitions and conformational switching are associated with characteristic flexibility and disorder indices in TRP and Kv channels

“…Indeed, this transition has been reported in several K- and Na-channels [ 13 ]. In the Shaker Kv channel, a short-lived 3 10 -helical structure has been well identified at the S4b segment during channel activation [ 63 , 64 ]. Experimental evidence also indicates that although this part of the protein in KCNQ1 channels (Kv7.1) is mainly α-helical, it has the potential to transit to 3 10 configurations depending on the milieu conditions [ 65 ].…”