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Appl. Environ. Microbiol., 11 1995, 3894-3903, Vol 61, No. 11
B Ottenwalder, T Kupke, S Brecht, V Gnau, J Metzger, G Jung and F Gotz
Gallidermin (Gdm) and epidermin (Epi) are highly homologous tetracyclic
polypeptide antibiotics that are ribosomally synthesized by a
Staphylococcus gallinarum strain and a Staphylococcus epidermidis strain,
respectively. These antibiotics are secreted into media and are
distinguished by the presence of the unusual amino acids lanthionine, 3-
methyllanthionine, didehydrobutyrine, and S-(2-aminovinyl)-D-cysteine,
which are formed by posttranslational modification. To study the substrate
specificities of the modifying enzymes and to obtain variants that exhibit
altered or new biological activities, we changed certain amino acids by
performing site-specific mutagenesis with the Gdm and Epi structural genes
(gdmA and epiA, respectively). S. epidermidis Tu3298/EMS6, an epiA mutant
of the Epi-producing strain, was used as the expression host. This mutant
synthesized Epi, Gdm, or analogs of these antibiotics when the appropriate
genes were introduced on a plasmid. No Epi or Gdm analogs were isolated
from the supernatant when (i) hydroxyamino acids involved in thioether
amino acid formation were replaced by nonhydroxyamino acids (S3N and S19A);
(ii) C residues involved in thioether bridging were deleted (delta C21, C22
and delta C22); or (iii) a ring amino acid was replaced by an amino acid
having a completely different character (G10E and Y20G). A strong decrease
in production was observed when S residues involved in thioether amino acid
formation were replaced by T residues (S16T and S19T). A number of
conservative changes at positions 6, 12, and 14 on the Gdm backbone were
tolerated and led to analogs that had altered biological properties, such
as enhanced antimicrobial activity (L6V) or a remarkable resistance to
proteolytic degradation (A12L and Dhb14P). The T14S substitution led to
simultaneous production of two Gdm species formed by incomplete
posttranslational modification (dehydration) of the S-14 residue. The fully
modified Dhb14Dha analog exhibited antimicrobial activity similar to that
of Gdm, whereas the Dhb14S analog was less active. Both peptides were more
sensitive to tryptic cleavage than Gdm was.
Copyright © 1995, American Society for Microbiology
Isolation and characterization of genetically engineered gallidermin and epidermin analogs
Mikrobielle Genetik, Universitat Tubingen, Germany.
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