SEQUENCE-SPECIFIC H-1 ASSIGNMENT AND SECONDARY STRUCTURE OF THE BACTERIOCIN AS-48 CYCLIC PEPTIDE

The bacteriocin AS-48 is a cationic peptide (7149 Da) having a broad a ntimicrobial spectrum, encoded by the 68 kb conjugative plasmid pMB2 f rom Enterococcus faecalis S-48. It is a unique peptide since it has a cyclic structure, which is achieved by the formation of a tail-head pe ptide bond after ribosomal synthesis (Galvez et al., 1989; Martinet-Bu eno et al., 1994; Samyn et al., 1994). Preliminary CD and calorimetric studies (data not shown) pointed towards a highly helical and very st able three dimensional structure. All the information gathered until n ow indicates that the target of AS-48 is the cytoplasmic membrane in w hich it opens channels,or pores, leading to dissipation of the proton motive force and cell death, which in some cases is also followed by b acterial lysis (Galvez et al., 1991). This peptide is a suitable tool for studying protein-membrane interactions, and it also offers promisi ng perspectives for biotechnological applications. Knowledge of the 3D structure of AS-48 is a first step in the conduct of further structur e-function studies. Here we report the complete H-1 NMR assignment of its proton resonances together with the resulting secondary structure pattern as prerequisites for the determination of a high-resolution 3D solution structure.