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

• Published in: Biochemistry (Easton) 1997-12, Vol.36 (49), p.15062-15072
• Main Authors: Fregeau Gallagher, Nancy L., Sailer, Miloslav, Niemczura, Walter P., Nakashima, Thomas T., Stiles, Michael E., Vederas, John C.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacteriocins - chemistry; Circular Dichroism; Hydrogen - chemistry; Lactobacillus - chemistry; Magnetic Resonance Spectroscopy; Micelles; Molecular Sequence Data; Phosphorylcholine - analogs & derivatives; Phosphorylcholine - chemistry; Protein Conformation; Sequence Homology, Amino Acid; Trifluoroethanol - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi971263h

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 α-helix conformation. A three-strand antiparallel β-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 α-helix. The implications of these structural features with regard to the antimicrobial mechanism of action and target recognition are discussed.