title: Two-dimensional rotational-echo double resonance of Val1-[1-13C]Gly2-[15N]Ala3-gramicidin A in multilamellar dimyristoylphosphatidylcholine dispersions.
abstract: The dipolar coupling between the Gly2 13C-1 carbon and Ala3 15N-amide nitrogen was used to investigate the conformation and dynamics of the Gly2-Ala3 13C-15N peptide bond in Val1-[1-13C]Gly2-[15N]Ala3-gramicidin A incorporated into multilamellar dispersions of dimyristoylphosphatidylcholine. Measurement of the 13C-15N dipolar coupling constant D of the labeled gramicidin in a powder and the effective dipolar coupling constant De in a multilamellar dispersion was accomplished by two-dimensional rotational-echo double-resonance (2D REDOR) NMR, a magic-angle spinning experiment designed to measure weak dipolar coupling constants. The magnitudes of D and De were measured by the mirror-symmetric form of 2D REDOR, and the signs of D and De were determined relative to the sign of the isotropic indirect spin-spin coupling constant J by the mirror-asymmetric form of 2D REDOR. From knowledge of the magnitudes of D and De, four possible values were calculated for the angle between the Gly2-Ala3 13C-15N peptide bond and the gramicidin helical axis. Additional knowledge of the signs of D and De permitted the set of possible values for the peptide bond angle to be reduced to a single angle and its supplement (64 degrees, 116 degrees). This information about the Gly2-Ala3 13C-15N peptide bond angle eliminates the double-stranded, helical dimers and the left-handed, single-stranded, beta 6.3 helical dimer but supports the right-handed, single-stranded, beta 6.3 helical dimer as the structural model for gramicidin in multilamellar dispersions.
authors.affiliation: Department of Chemistry, Washington University, St. Louis, Missouri 63130.
authors.forename: A W
authors.initials: AW
authors.lastname: Hing
authors.forename: J
authors.initials: J
authors.lastname: Schaefer
mesh_terms: D000595:Amino Acid Sequence; D002247:Carbon Isotopes; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D004134:Dimyristoylphosphatidylcholine; D006096:Gramicidin / Q000737:chemistry*; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012996:Solutions
chemical_list: D002247:Carbon Isotopes; D046911:Macromolecular Substances; D009587:Nitrogen Isotopes; D012996:Solutions; D006096:Gramicidin; D004134:Dimyristoylphosphatidylcholine