抄録
A protein called Ci-VSP (Voltage Sensor containing Phosphatase) has recently been reported (Murata et al, Nature 2005). VSPs have ion channel like transmembrane segments from S1 to S4 as the voltage sensor domain and the C-terminal cytoplasmic domain. It exhibits phosphatase activity in a voltage dependent manner. We have previously compared zebrafish ortholog of VSP (Z-VSP) with Ci-VSP and found that Z-VSP shows more robust charge movements in mammalian heterologous expression than Ci-VSP. To understand voltage-sensing mechanisms of VSP, we focused on the double mutant of Z-VSP in which two arginine residues were inserted into the S4 (DM). This shows negative shift of the Q-V curve (threshold was around -40 mV). Furthermore, DM showed biphasic profile of the Q-V curve that could not be fitted by a single Boltzmann equation: the movement of the voltage senor saturates around at 100 mV but then it increases as the membrane potential is more depolarized. Such biphasic profile of the Q-V curve did not depend on the phosphatase activity as examined from C302S mutant. This exhibited the threshold of charge movement even more negative (around -60 mV) and the simple Q-V curve that can be fitted with the single Boltzmann equation. These results suggest that the C-terminal domain but not its enzyme activity affects charge movement probably through exerting some constraint on the movement of the VS domain. [J Physiol Sci. 2006;56 Suppl:S154]
