Abstract
Voltage-sensing domain (VSD) is crucial for the function of voltage dependent ion channels. Recent advancements of structural studies on the voltage dependent ion channels have revealed various structural features of VSD; however, the movement and conformational change of segments S1-S4 within VSD in response to membrane depolarization are still under debate. We have previously shown that KCNE1, which is an auxiliary subunit for KCNQ1 K + channel, stabilizes VSD in the down state and proposed a possible interaction between VSD and KCNE1. In the present study, we found that some of the cysteine mutants of S4 domain (I227C, R228C, G229C, I230C, R231C, F232C and L233C) were trapped in the open state after depolarization in the absence of KCNE1. There are two endogenous cysteine residues in the transmembrane region, C136 on S1 segment and C331 on S6 segment, therefore, we suspected either of them might form a disulfide bond with introduced cysteine residue on S4 segment. By substituting each cysteine with alanine, we identified that C136 made a disulfide bond with the exogenous cysteine residue on S4 segment. Interestingly, except for G229C, the disulfide bode was not formed by co-expressing KCNE1. These results suggest that S1 segment interacts with S4 segment in the absence of KCNE1 and that KCNE1 disrupts the interaction between S1 and S4. KCNE1 might change the conformation of VSD and eventually affect the equilibrium between the up state and down state of VSD. [J Physiol Sci. 2008;58 Suppl:S76]
