Three-dimensional structure of the two peptides that constitute the two-peptide bacteriocin lactococcin G

The three-dimensional structures of the two peptides, lactococcin G-α (LcnG-α; contains 39 residues) and lactococcin G-β (LcnG-β, contains 35 residues), that constitute the two-peptide bacteriocin lactococcin G (LcnG) have been determined by nuclear magnetic resonance (NMR) spectroscopy in the presence of DPC micelles and TFE. In DPC, LcnG-α has an N-terminal α-helix (residues 3–21) that contains a GxxxG helix–helix interaction motif (residues 7–11) and a less well defined C-terminal α-helix (residues 24–34), and in between (residues 18–22) there is a second somewhat flexible GxxxG-motif. Its structure in TFE was similar. In DPC, LcnG-β has an N-terminal α-helix (residues 6–19). The region from residues 20 to 35, which also contains a flexible GxxxG-motif (residues 18–22), appeared to be fairly unstructured in DPC. In the presence of TFE, however, the region between and including residues 23 and 32 formed a well defined α-helix. The N-terminal helix between and including residues 6 and 19 seen in the presence of DPC, was broken at residues 8 and 9 in the presence of TFE. The N-terminal helices, both in LcnG-α and -β, are amphiphilic. We postulate that LcnG-α and -β have a parallel orientation and interact through helix–helix interactions involving the first GxxxG (residues 7–11) motif in LcnG-α and the one (residues 18–22) in LcnG-β, and that they thus lie in a staggered fashion relative to each other.