Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Friday Speaker Abstracts

Coupling Mechanisms of Voltage-sensing Phosphatase Akira Kawanabe 1 , Yuka Jinno 1 , Souhei Sakata 2 , Yasushi Okamura 1 . 2 Osaka Medical College, Takatsuki, Japan. 1 Graduate School of Medicine, Osaka University, Suita, Osaka, Japan, Biological membrane provides environment both for electrical signal and chemical signal. Phosphoinositides (PIs) are phospholipids playing roles not only in chemical signal but also in electrical signal. PIs directly regulate many types of ion channels and transporters as known in cellular events such as modulation of membrane excitability, secretion and contraction. In turn, electrical signal influences profile of lipids. Voltage-sensing phosphatase, VSP, provides one of the molecular mechanisms underlying such electrochemical coupling. VSP contains the voltage sensor domain with similar structure to that in voltage-gated ion channels. The cytoplasmic enzyme region of VSP shows remarkable structural similarity to tumor suppressor phosphatase, PTEN. VSP exhibits depolarization-activated phosphatase activity toward three species of PIs. PTEN dephosphorylates exclusively 3-phosphate of inositol ring, whereas VSP shows broader preference: it dephosphorylates both 3-phosphate and 5-phosphate. In contrast with voltage-gated ion channels where multiple voltage sensors cooperate to regulate their central pore, VSP has single voltage sensor domain that regulates the downstream enzyme. Thus VSP raises several fundamental questions; whether the coupling mechanisms from voltage sensor is shared between voltage-gated ion channels and VSP, and whether regulatory mechanisms of enzyme are shared between PTEN and VSP. In this talk, we present recent view about mechanisms of the electrochemical coupling in VSP. By labeling single amino acid by fluorescent unnatural amino acid, Anap to Ci (Ciona intestinalis)-VSP heterologously expressed in Xenopus oocyte, we show evidence that enzyme takes multiple states probably coupled with distinct states of voltage sensor. We also show recent findings of a novel critical site for coupling between the voltage sensor domain and the phosphatase domain.

35