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J Gen Physiol. 2013 Nov;142(5):543-55. doi: 10.1085/jgp.201310993. Epub 2013 Oct 14.

Sensing charges of the Ciona intestinalis voltage-sensing phosphatase.

Author information

1
Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, VA 23298.

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.

PMID:
24127524
PMCID:
PMC3813379
DOI:
10.1085/jgp.201310993
[Indexed for MEDLINE]
Free PMC Article

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