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

J. Biol. Chem., Vol. 283, Issue 32, 22233-22243, August 8, 2008

This Article Full Text Full Text (PDF) All Versions of this Article: 283/32/22233    most recent M802074200v1 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 Google Scholar Google Scholar Articles by Sun, H. Articles by Koeppe, R. E. Search for Related Content PubMed PubMed Citation Articles by Sun, H. Articles by Koeppe, R. E., II Social Bookmarking                      What's this?

The Preference of Tryptophan for Membrane Interfaces

INSIGHTS FROM N-METHYLATION OF TRYPTOPHANS IN GRAMICIDIN CHANNELS^*

Haiyan Sun, Denise V. Greathouse, Olaf S. Andersen¹, and Roger E. Koeppe, II²

From the Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701 and the Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York 10065

To better understand the structural and functional roles of tryptophan at the membrane/water interface in membrane proteins, we examined the structural and functional consequences of Trp 1-methyl-tryptophan substitutions in membrane-spanning gramicidin A channels. Gramicidin A channels are miniproteins that are anchored to the interface by four Trps near the C terminus of each subunit in a membrane-spanning dimer. We masked the hydrogen bonding ability of individual or multiple Trps by 1-methylation of the indole ring and examined the structural and functional changes using circular dichroism spectroscopy, size exclusion chromatography, solid state ²H NMR spectroscopy, and single channel analysis. N-Methylation causes distinct changes in the subunit conformational preference, channel-forming propensity, single channel conductance and lifetime, and average indole ring orientations within the membrane-spanning channels. The extent of the local ring dynamic wobble does not increase, and may decrease slightly, when the indole NH is replaced by the non-hydrogen-bonding and more bulky and hydrophobic N-CH₃ group. The changes in conformational preference, which are associated with a shift in the distribution of the aromatic residues across the bilayer, are similar to those observed previously with Trp Phe substitutions. We conclude that indole N-H hydrogen bonding is of major importance for the folding of gramicidin channels. The changes in ion permeability, however, are quite different for Trp Phe and Trp 1-methyl-tryptophan substitutions, indicating that the indole dipole moment and perhaps also ring size and are important for ion permeation through these channels.

Received for publication, March 14, 2008 , and in revised form, June 3, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grants RR15569 and GM70971. 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 may be addressed: 1300 York Ave., New York, NY 10065. Fax: 212-746-8369; E-mail: sparre{at}med.cornell.edu.

² To whom correspondence may be addressed: 119 Chemistry Bldg., Fayetteville, AR 72701. Fax: 479-575-4049; E-mail: rk2{at}uark.edu.

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