Title

Structural model of the voltage-sensing domain in Ci-VSP

ORCiD

Carlos A. Villalba-Galea: 0000-0002-6489-4651

Document Type

Poster

Conference Title/Conference Publication

Biophysical Journal

Organization

Biophysical Society 54th Annual Meeting

Location

San Francisco, CA

Conference Dates

February 20-24, 2010

Date of Presentation

2-20-2010

ISSN

0006-3495

Volume

98

Issue

3, Supplement 1

DOI

10.1016/j.bpj.2009.12.3533

First Page

645a

Abstract

CiVSP is a voltage sensor-containing phosphatase whose N-terminal comprises a voltage sensing domain (VSD). Its lack of a conduction pore makes CiVSP an excellent model to study conformational changes in VSDs. Although the structure of CiVSP's VSD is unknown, it shares sequence homology with the VSDs of potassium channels with known crystal structures. We have taken advantage of this similarity to generate a model of CiVSP's VSD using the program ESyPred3D. The stability of the model was tested using the molecular dynamics simulation package, NAMD. After equilibration, we imposed an electric field to mimic a membrane potential of −200mV at 300K for a total simulation time of 20ns. One feature of the model is that residues R223 to R229 adopt a 3-10 helical structure with polar residues facing into the protein core. Meanwhile, water molecules in the interior of the helical bundle form an hourglass-shaped profile resembling those seen in Kv1.2 simulations. The water crevices are separated by a hydrophobic plug limited outside by R223 interacting with L155 and inside by R226 interacting with D159. These interactions serve as water barriers that focus the electric field. Experimentally, we have observed that the CiVSP mutant R217Q R223H produces a proton current at negative potentials. Simulations of the present model carrying these mutations effectively displayed a narrowing of the hydrophobic plug, allowing water molecules from the top and bottom crevices to come into close proximity, while R226 prevents the collapse of the hydrophobic plug. This effect might create the optimal conditions for proton conduction. We conclude that our model of the ‘resting’state of CiVSP's VSD contains features that are consistent with experimental observations and is a good starting point to study conformational changes in VSDs.