title: Three-dimensional structure of leucocin A in trifluoroethanol and dodecylphosphocholine micelles: spatial location of residues critical for biological activity in type IIa bacteriocins from lactic acid bacteria.
abstract: The first three-dimensional structure of a type IIa bacteriocin from lactic acid bacteria is reported. Complete 1H resonance assignments of leucocin A, a 37 amino acid antimicrobial peptide isolated from the lactic acid bacterium Leuconostoc gelidum UAL187, were determined in 90% trifluoroethanol (TFE)-water and in aqueous dodecylphosphocholine (DPC) micelles (1:40 ratio of leucocin A:DPC) using two-dimensional NMR techniques (e.g., DQF-COSY, TOCSY, NOESY). Circular dichroism spectra, NMR chemical shift indices, amide hydrogen exchange rates, and long-range nuclear Overhauser effects indicate that leucocin A adopts a reasonably well defined structure in both TFE and DPC micelle environments but exists as a random coil in water or aqueous DMSO. Distance geometry and simulated annealing calculations were employed to generate structures for leucocin A in both lipophilic media. While some differences were noted between the structures calculated for the two different solvent systems, in both, the region encompassing residues 17-31 assumes an essentially identical amphiphilic alpha-helix conformation. A three-strand antiparallel beta-sheet domain (residues 2-16), anchored by the disulfide bridge, is also observed in both media. In TFE, these two regions have a more defined relationship relative to each other, while, in DPC micelles, the C-terminus is folded back onto the alpha-helix. The implications of these structural features with regard to the antimicrobial mechanism of action and target recognition are discussed.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
authors.forename: N L
authors.initials: NL
authors.lastname: Fregeau Gallagher
authors.forename: M
authors.initials: M
authors.lastname: Sailer
authors.forename: W P
authors.initials: WP
authors.lastname: Niemczura
authors.forename: T T
authors.initials: TT
authors.lastname: Nakashima
authors.forename: M E
authors.initials: ME
authors.lastname: Stiles
authors.forename: J C
authors.initials: JC
authors.lastname: Vederas
mesh_terms: D000595:Amino Acid Sequence; D001430:Bacteriocins / Q000737:chemistry*; D002942:Circular Dichroism; D006859:Hydrogen / Q000737:chemistry; D007778:Lactobacillus / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D008969:Molecular Sequence Data; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000737:chemistry; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D014270:Trifluoroethanol / Q000737:chemistry*
chemical_list: D001430:Bacteriocins; D008823:Micelles; D010767:Phosphorylcholine; C028810:dodecylphosphocholine; D014270:Trifluoroethanol; D006859:Hydrogen