Cooperative Interactions Between R531 and Acidic Residues in the Voltage Sensing Module of hERG1 Channels

Abstract

HERG1 K⁺ channels are critical for modulating the duration of the cardiac action potential. The role of hERG1 channels in maintaining electrical stability in the heart derives from their unusual gating properties: slow activation and fast inactivation. HERG1 channel inactivation is intrinsically voltage sensitive and is not coupled to activation in the same way as in the Shaker family of K⁺ channels. We recently proposed that the S4 transmembrane domain functions as the primary voltage sensor for hERG1 activation and inactivation and that distinct regions of S4 contribute to each gating process. In this study, we tested the hypothesis that S4 rearrangements underlying activation and inactivation gating may be associated with distinct cooperative interactions between a key residue in the S4 domain (R531) and acidic residues in neighboring regions (S1 – S3 domains) of the voltage sensing module. Using double-mutant cycle analysis, we found that R531 was energetically coupled to all acidic residues in S1-S3 during activation, but was coupled only to acidic residues near the extracellular portion of S2 and S3 (D456, D460 and D509) during inactivation. We propose that hERG1 activation involves a cooperative conformational change involving the entire voltage sensing module, while inactivation may involve a more limited interaction between R531 and D456, D460 and D509.

Molecular Coupling in the Human ether-a-go-go-related gene-1 (hERG1) K+ Channel Inactivation Pathway

“…Data plots, Boltzmann fits, and ⌬⌬G calculations and were performed using Origin 7.0 (OriginLabs Corp., Northampton, MA). In earlier works (23,24), we used a threshold value of ⌬⌬G 0 Ն 0.5 kcal-mol Ϫ1 to denote a significant mutation-induced perturbation in inactivation gating for residues distant from the selectivity filter/pore helix. Given the importance of the pore helix structure to inactivation gating, we reasoned that many mutations in this region might alter inactivation gating.…”

The S1 helix critically regulates the finely tuned gating of Kv11.1 channels

“…This suggests that the S1 helix likely forms a complex network of intra-subunit interactions with these two helices. In Kv11.1 channels, as well as in many other Kv family members, negatively charged residues in the S1, S2, and S3 helices are thought to form charge-charge interactions with positively charged residues within the S4 helix (28,29,31,49). This network of charge paired interactions stabilizes the S4 voltage sensor and fine tunes the voltage sensitivity of channel activation.…”

Voltage-Dependent Gating of hERG Potassium Channels

“…Together, these results suggest that the arginines in the middle of S4 may be involved in interactions that stabilize the open state or, alternatively, in facilitating transitions leading to the open state. Overall, R2 and R3 were shown to have the largest effects on both the voltage-dependence and rate of channel opening (Subbiah et al, 2004, 2005; Piper et al, 2008). As the analogous residues in Kv1.2 have been suggested to form salt-bridges within the activated conformation of the voltage-sensing domain seen in the Kv1.2 crystal structure (Long et al, 2005a), these observations have been considered to suggest that interactions involving R2 and R3 are particularly important in stabilizing partially activated states and the slow activation of hERG (Piper et al, 2005; Subbiah et al, 2005).…”