Journal Article

Three-Dimensional Structure at 0.86 Å of the Uncomplexed Form of the Transmembrane Ion Channel Peptide Gramicidin A

Langs, David A.

1988

Overview

The crystal structure of the uncomplexed orthorhombic form of gramicidin A has been determined at 120 K and at 0.86 angstrom resolution. The pentadecapeptide crystallizes as a left-handed antiparallel double-stranded helical dimer with 5.6 amino acid residues per turn. The helix has an overall length of 31 angstroms and an average inner channel diameter of 4.80 angstroms. The channel of this crystalline form is void of ions or solvent molecules. The channel diameter varies form a minimum of 3.85 angstroms to a maximum of 5.47 angstroms and contains three pockets where the cross-channel contacts are 5.25 angstroms or greater. The range of variation seen for the φ and ψ torsion angles of the backbone of the helix suggests that these potential ion binding sites can be induced to travel the length of the channel in a peristaltic manner by cooperatively varying these angles. The indole rings of the eight tryptophan residues of the dimer are overlapped in three separate regions on the outer surface of the helix when viewed down the barrel of the channel. This arrangement would permit long-chained lipid molecules to nest parallel to the outer channel surface between these protruding tryptophan regions and act like molecular splines to constrain helical twist deformations of the channel.

• Publisher: The American Association for the Advancement of Science,American Association for the Advancement of Science
• Subject: Amino acids / Atoms / Binding Sites / Biological and medical sciences / Crystal structure / Crystalline structure / Crystallography / Dimers / Fundamental and applied biological sciences. Psychology / Gramicidin / Hydrogen bonds / Ion Channels / Ions / Membrane Proteins / Models, Molecular / Molecular biophysics / Molecules / Protein Conformation / Solvents / Structure in molecular biology