Eukaryotic cells have voltage-gated ion channels that are directly activated by voltage but never by light. Voltage-gated ion channels contain a voltage-sensing domain (VSD) that responds to changes in membrane potential by gating the pore domain. VSD are functionally independent domains within canonical voltage-activated ion channels, but are also components of voltage-sensing enzymes and can also form ion channels. Several strategies have been used to enable light regulation of ion channels that are not intrinsically light sensitive and these channels have been successfully used to control neuronal activity (Gorostiza & Isacoff 2007). In the case of voltage-gated potassium (Kv) channels, photoswitchable molecules have been described but they specifically act as covalently tethered channel blockers (Horn et al., 2000). To date, photo-regulation of VSDs has not been reported. Photoswitchable VSD would constitute an exclusive independent structure to remotely control voltage-sensing proteins. We expect voltage-sensing proteins will be rapidly and reversibly activated by light, which has potential use as a noninvasive method to study motion charging shape of VSD in vitro and in vivo. This project aims to develop a new photoswitchable light-activated VSD by incorporating an azobenzene chromophore into the VSD of Shaker Kv channel. Although the X-ray crystallographic structures of prokaryotic and same as eukaryotic potassium channels were recently published, the position and the molecular movement of the voltage sensor in the activated or deactivated state are still controversial. As a long term aim of this project, this approach could be extended to the recently cloned and described VSD proteins such as Ci-VSP and Hv1 (Murata el al., 2005; Sasaki et al., 2006; Ramsey et al., 2006). Light activation of the voltage sensor would elucidate movements within this structure and report on the gating mechanisms of voltage-activated ion channels and VSD-containing proteins.
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