Electrostatic Interactions in the Voltage Sensor of Kv7.1 and Iks Channels
Date of Award
Doctor of Philosophy (PhD)
Ion channels are integral proteins found in the membranes of every cell in our body that underlie electrical impulses in a variety of tissues and organs, including the heart and the brain. In the heart, IKs potassium channels generate an important repolarizing cardiac current that contributes to the termination of the cardiac action potential. Congenital mutations that disrupt the function of IKs can lead to cardiac arrhythmias and sudden death. The IKs channel consists of the voltage gated potassium channel Kv7.1 coassembled with the single transmembrane auxiliary peptide KCNE1. Although Kv7.1 forms a functional channel, the properties of Kv7.1 are profoundly modulated by KCNE1. Kv7.1, like all voltage gated potassium channels, is composed of two domains: the voltage-sensing domain (VSD) and the pore. The VSD of Kv7.1 is comprised of four transmembrane helices (S1-S4), with conserved basic residues in S4 moving across the membrane in response to changes in transmembrane voltage and conserved acidic residues in S2 and S3 that may stabilize S4. The movement of S4 is the key initial step of the gating process that opens the pore gate and allows passage of potassium ions. The goal of this study is to determine the nature of electrostatic interactions in the VSD of Kv7.1 and assess how KCNE1 modulates these interactions. The first study examines electrostatic interactions in Kv7.1 and uses these interactions as a measure of S4 movement. By mapping out electrostatic interactions between an acidic residue in S2 (E160/E1) and basic residues in S4, the extent of S4 motion can be approximated. The results are consistent with E1 interacting with R1 in the resting state of the VSD and E1 interacting R4 in the activated state. The second study investigates the mechanism by which KCNE1 affects the VSD to alter Kv7.1 function. Systematic mutations in the VSD of Kv7.1 and expression of these mutants with and without KCNE1 highlight a region in the lower part of S4 that behaves differently in the presence of KCNE1. These results suggest that KCNE1 alters interactions in the lower region of S4 and enhances extracellular exposure to the top of S4. Thus, KCNE1 remodels the VSD of Kv7.1, which may contribute to its modulatory effect on channel function.
Christopher Lingle, Yoram Rudy, Lawrence Salkoff