Pep5 is a tricyclic
peptide antibiotic which contains the unusual
amino acids dehydrobutyrine,
lanthionine and 3-methyllanthionine. It is matured from a 60-amino-acid precursor
peptide (pre-Pep5) deduced from the sequence of the structural gene pepA. To study the biosynthesis of Pep5 we tried to isolate the primary translation product. We identified a
peptide in
crude extracts of the Pep5-producing Staphylococcus epidermidis strain using
antibodies raised against a synthetic 26-residue
peptide representing the
leader peptide region of pre-Pep5. The putative precursor was purified by reversed-phase HPLC. The isolated
peptide did not react with
antibodies directed against a C-terminal fragment of mature Pep5 containing two
sulfide bridges. Neither
lanthionine nor 3-methyllanthionine was detected in
amino acid analysis of the isolated precursor. Its amino acid sequence was identical with the sequence predicted from pepA, but Edman degradation stopped at the first
threonine residue of the prolantibiotic region indicating a posttranslational modification at this position. The molecular mass of the isolated
peptide was 6575.4 +/- 1.7 Da, determined by ion-spray mass spectrometry. This is in agreement with a molecule being dehydrated at the four
threonine and the two
serine residues in the propeptide region; such a
peptide has a calculated molecular mass of 6576.7 Da. The results strongly suggest that maturation of the
lantibiotic Pep5 is initiated by selective
dehydration of hydroxyamino
acids in the propeptide region of the primary translation product and that
thioether ring formation is not closely linked to
dehydration.