title: Sensing charges of the Ciona intestinalis voltage-sensing phosphatase.
abstract: Voltage control over enzymatic activity in voltage-sensitive phosphatases (VSPs) is conferred by a voltage-sensing domain (VSD) located in the N terminus. These VSDs are constituted by four putative transmembrane segments (S1 to S4) resembling those found in voltage-gated ion channels. The putative fourth segment (S4) of the VSD contains positive residues that likely function as voltage-sensing elements. To study in detail how these residues sense the plasma membrane potential, we have focused on five arginines in the S4 segment of the Ciona intestinalis VSP (Ci-VSP). After implementing a histidine scan, here we show that four arginine-to-histidine mutants, namely R223H to R232H, mediate voltage-dependent proton translocation across the membrane, indicating that these residues transit through the hydrophobic core of Ci-VSP as a function of the membrane potential. These observations indicate that the charges carried by these residues are sensing charges. Furthermore, our results also show that the electrical field in VSPs is focused in a narrow hydrophobic region that separates the extracellular and intracellular space and constitutes the energy barrier for charge crossing.
authors.affiliation: Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Villalba-Galea
authors.forename: Ludivine
authors.initials: L
authors.lastname: Frezza
authors.forename: Walter
authors.initials: W
authors.lastname: Sandtner
authors.forename: Francisco
authors.initials: F
authors.lastname: Bezanilla
mesh_terms: D000818:Animals; D002938:Ciona intestinalis / Q000201:enzymology* / Q000235:genetics*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011522:Protons
chemical_list: D011522:Protons; C509671:voltage-sensor-containing phosphatase, Ciona intestinalis; D010744:Phosphoric Monoester Hydrolases