STRUCTURE OF AN ISOLATED GRAMICIDIN-A DOUBLE HELICAL SPECIES BY HIGH-RESOLUTION NUCLEAR-MAGNETIC-RESONANCE

A conformational species of gramicidin A has been isolated in dioxane by high pressure liquid chromatography and characterized by circular dichroism and two-dimensional proton nuclear magnetic resonance. Double-quantum filtered two-dimensional correlation spectroscopy, two-dimensional homonuclear Hartman Hahn spectroscopy and two-dimensional nuclear Overhauser effect spectra at 500 MHz were used to obtain virtually complete proton assignments and produce 192 distance constraints. Protocols to determine the state of aggregation, monomer-specific assignment of nuclear Overhauser enhancement values, hydrogen bonding pattern and helix handedness are described. A distance geometry/ simulated annealing routine was used to generate well-defined backbone and side-chain structures. The species isolated is a right-handed intertwined double helix, with approximately 5·7 residues per turn. Unique values for helical dimensions are also specified. © 1992.