Spatial distribution of spin-labeled trichogin GA IV in the Gram-positive bacterial cell membrane determined from PELDOR data

Trichogin GA IV is one of the shortest acyclic linear polypeptide antibiotics of fungal origin, characterized by the presence of three alpha-amino isobutyric acid residues, an N-octanoyl group and an amino alcohol at the C terminus. Its antibiotic activity is generally thought to be based on its self-assembling and membrane-modifying properties. The technique of double electron-electron resonance in electron spin echo is used to study the spatial distribution of spin-labeled [TOAC-4]trichogin GA IV analog bound to the cell membrane of the Gram-positive bacterium Micrococcus luteus. The intermolecular dipole-dipole spin-spin interaction of TOAC spin labels has been experimentally studied at 77 K in glassy dispersions of the spherical cell particles. It is shown that the nonaggregated peptide molecules are distributed at the cytoplasmic membrane. Two possible distribution models are proposed: (i) the peptide molecules are randomly distributed on both inner and outer membrane surfaces with a distance between the surfaces of 7 run, (ii) the molecules are randomly distributed in a layer up to 2.4 mn from the external surface of the membrane.