An in vivo study of novel bioactive peptides that inhibit the growth of Escherichia coli.

We have created a system in which synthetically produced novel bioactive peptides can be expressed in vivo in Escherichia coli. Twenty thousand of these peptides were screened and 21 inhibitors were found that could inhibit the growth of E. coli on minimal media. The inhibitors could be placed into one of two groups, 1-day inhibitors, which were partially inhibitory, and 2-day inhibitors, which were completely inhibitory. Sequence analysis showed that two of the most potent inhibitors were actually peptide-protein chimeras in which the peptides had become fused to the 63 amino acid Rop protein which was also contained in the expression vector used in this study. Given that Rop is known to form an incredibly stable structure, it could be serving as a stabilizing motif for these peptides. Sequence analysis of the predicted coding regions from the next 10 most inhibitory peptides showed that four of the 10 peptides contained one or more proline residues either at or very near the C-terminal end of the peptide which could act to prevent degradation by peptidases. Collectively, based on what we observed in our screen of synthetic bioactive peptides that could prevent the growth of E. coli and what has been learned from structural studies of naturally occurring bioactive peptides, the presence of a stabilizing motif seems to be important for small peptides, if they are to be biologically active.