The preference of tryptophan for membrane interfaces: Insights from N-methylation of tryptophans in gramicidin channels Academic Article uri icon

Overview

MeSH Major

  • Gramicidin
  • Ion Channels
  • Membrane Proteins
  • Tryptophan

abstract

  • 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 (2)H 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-CH(3) 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.

publication date

  • August 8, 2008

Research

keywords

  • Academic Article

Identity

Language

  • eng

PubMed Central ID

  • PMC2494914

Digital Object Identifier (DOI)

  • 10.1074/jbc.M802074200

PubMed ID

  • 18550546

Additional Document Info

start page

  • 22233

end page

  • 43

volume

  • 283

number

  • 32