3-DIMENSIONAL STRUCTURE OF LEUCOCIN-A IN TRIFLUOROETHANOL AND DODECYLPHOPHOCHOLINE MICELLES - SPATIAL LOCATION OF RESIDUES CRITICAL FOR BIOLOGICAL-ACTIVITY IN TYPE IIA BACTERIOCINS FROM LACTIC-ACID BACTERIA

The first three-dimensional structure of a type IIa bacteriocin from l actic acid bacteria is reported. Complete H-1 resonance assignments of leucocin A, a 37 amino acid antimicrobial peptide isolated from the l actic acid bacterium Leuconostoc gelidum UAL187, were determined in 90 % trifluoroethanol (TFE)-water and in aqueous dodecylphosphocholine (D PC) 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-r ange nuclear Overhauser effects indicate that leucocin A adopts a reas onably well defined structure in both TFE and DPC micelle environments hut exists as a random coil in water or aqueous DMSO, Distance geomet ry and simulated annealing calculations were employed to generate stru ctures for leucocin A in both lipophilic media. While some differences were noted between the structures calculated for the two different so lvent systems, in both, the region encompassing residues 17-31 assumes an essentially identical amphiphilic alpha-helix conformation. A thre e-strand antiparallel beta-sheet domain (residues 2-16), anchored by t he disulfide bridge, is also observed in both media, Ln TFE, these two regions have a more defined relationship relative to each other, whil e, in DPC micelles, the C-terminus is folded back onto the alpha-helix , The implications of these structural feature's with regard to the an timicrobial mechanism of action and target recognition are discussed.