Internal Switch Gates Phosphatase Activity of VSP

Abstract

Voltage regulation is responsible for a host of processes in the cell from muscle contraction to neuronal action potentials. In the Ciona intestinalis voltage-sensing phosphatase (Ci-VSP)1, voltage is responsible for controlling lipid phosphatase activity. How this happens is still not known. To address this, we have solved seven crystal structures of the cytosolic fragment of Ci-VSP. The structures reveal three active site conformations, one where the active site is blocked, one where the active site is open and one where the active site is bound with substrate. These three conformations show that the active site is gated. Activity assays on structure-based mutants show that the gate is involved in catalytic turnover as well as substrate specificity. A residue from the C2 domain that lines the active site in Ci-VSP, but not in the homologous phosphatase PTEN, also contributes to selectivity. A potential interaction between the segment of the protein that gates the active site and the inter-domain linker between the voltage sensing domain and the phosphatase suggests a model for coupling the voltage sensor to activity. The results indicate that voltage regulates enzyme activity by gating the active site.1. Murata, Y., et al, (2005) Nature 435, 1239-1243.