1. Howard Hughes Medical Institute and Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, 1230 York Avenue, New York, New York 10021,USA
2. Skirball Institute of Biomolecular Medicine, New York University Medical Center, 540 First Avenue, New York, New York 10016,USA

Correspondence to: Roderick MacKinnon¹ Email: mackinn@rockefeller.edu
The electron microscopy map has been deposited with European Bioinformatics Institute (http://www.ebi.ac.uk/msd/emd-2771.map).

Abstract

Voltage-dependent ion channels serve as field-effect transistors by opening a gate in response to membrane voltage changes¹. The gate's response to voltage is mediated by voltage sensors², which are arginine-containing structures that must move with respect to the membrane electric field. We have analysed by electron microscopy a voltage-dependent K⁺ channel from Aeropyrum pernix (KvAP)³. Fab fragments were attached to 'voltage sensor paddles' and identified in the electron microscopy map at 10.5 Å resolution. The extracellular surface location of the Fab fragments in the map is consistent with the membrane-depolarized, open conformation of the channel in electrophysiological experiments. Comparison of the map with a crystal structure⁴ demonstrates that the voltage sensor paddles are 'up' (that is, near the channel's extracellular surface) and situated at the protein–lipid interface. This finding supports the hypothesis that in response to changes in voltage the sensors move at the protein–lipid interface⁵ rather than in a gating pore surrounded by protein^{6, 7}.

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