HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

J. Biol. Chem., Vol. 282, Issue 11, 8044-8051, March 16, 2007

This Article Full Text Full Text (PDF) All Versions of this Article: 282/11/8044    most recent M611334200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Santarelli, V. P. Articles by Ahern, C. A. Search for Related Content PubMed PubMed Citation Articles by Santarelli, V. P. Articles by Ahern, C. A. Social Bookmarking                      What's this?

A Cation- Interaction Discriminates among Sodium Channels That Are Either Sensitive or Resistant to Tetrodotoxin Block^*

Vincent P. Santarelli, Amy L. Eastwood, Dennis A. Dougherty, Richard Horn, and Christopher A. Ahern¹

From the Department of Molecular Physiology and Biophysics, Institute of Hyperexcitability, Jefferson Medical College, Philadelphia, Pennsylvania 19107 and the Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125

Voltage-gated sodium channels control the upstroke of the action potential in excitable cells of nerve and muscle tissue, making them ideal targets for exogenous toxins that aim to squelch electrical excitability. One such toxin, tetrodotoxin (TTX), blocks sodium channels with nanomolar affinity only when an aromatic Phe or Tyr residue is present at a specific location in the external vestibule of the ion-conducting pore. To test whether TTX is attracted to Tyr⁴⁰¹ of Na_V1.4 through a cation- interaction, this aromatic residue was replaced with fluorinated derivatives of Phe using in vivo nonsense suppression. Consistent with a cation- interaction, increased fluorination of Phe⁴⁰¹, which reduces the negative electrostatic potential on the aromatic face, caused a monotonic increase in the inhibitory constant for block. Trifluorination of the aromatic ring decreased TTX affinity by 50-fold, a reduction similar to that caused by replacement with the comparably hydrophobic residue Leu. Furthermore, we show that an energetically equivalent cation- interaction underlies both use-dependent and tonic block by TTX. Our results are supported by high level ab initio quantum mechanical calculations applied to a model of TTX binding to benzene. Our analysis suggests that the aromatic side chain faces the permeation pathway where it orients TTX optimally and interacts with permeant ions. These results are the first of their kind to show the incorporation of unnatural amino acids into a voltage-gated sodium channel and demonstrate that a cation- interaction is responsible for the obligate nature of an aromatic at this position in TTX-sensitive sodium channels.

Received for publication, December 11, 2006 , and in revised form, January 11, 2007.

^* This work was supported by Grants GM079427 and NS34407 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 215-503-6721; Fax: 215-503-2073; E-mail: Christopher.Ahern{at}jefferson.edu.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				I. Bruhova, D. B. Tikhonov, and B. S. Zhorov Access and Binding of Local Anesthetics in the Closed Sodium Channel Mol. Pharmacol., October 1, 2008; 74(4): 1033 - 1045. [Abstract] [Full Text] [PDF]

				C. A. Ahern, A. L. Eastwood, D. A. Dougherty, and R. Horn Electrostatic Contributions of Aromatic Residues in the Local Anesthetic Receptor of Voltage-Gated Sodium Channels Circ. Res., January 4, 2008; 102(1): 86 - 94. [Abstract] [Full Text] [PDF]