Voltage-Regulated Phosphatase

Abstract

A survey of the genome of the sea squirt Ciona intestinalis turned up an unusual molecule with sequence similarity to both ion channels and phosphatases, dubbed Ci-VSP, short for C. intestinalis voltage sensor-containing phosphatase. Murata et al. characterized the protein and showed that it is in fact a transmembrane phosphatase and that its enzymatic activity can be controlled by changes in voltage across the plasma membrane. The sequence similarity of Ci-VSP to channels includes similarity to the voltage-sensing portions of voltage-regulated potassium channels. The catalytic region of Ci-VSP resembles that of the lipid phosphatase PTEN, and the authors showed that Ci-VSP dephosphorylated phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P 3 ] in vitro. Murata et al. expressed inwardly rectifying potassium channels [which are regulated by PtdIns(4,5)P 2 ] as sensors for lipid phosphatase activity in Xenopus oocytes that also expressed Ci-VSP. These experiments revealed voltage-dependent regulation of Ci-VSP activity. A great deal of effort has gone into understanding how movements of the voltage sensor of potassium channels regulate channel opening. The results of Murata et al. open a new area for investigation into the mechanisms by which similar segments may be used to control enzymatic activity. Y. Murata, H. Iwasaki, M. Sasaki, K. Inaba, Y. Okamura, Phosphoinositide phosphatase activity coupled to an intrinsic voltage sensor. Nature 435 , 1239-1243 (2005). [PubMed]