Tracheal
cytotoxin (TCT) is a
disaccharide-tetrapeptide released by Bordetella pertussis, the causative agent of
pertussis (
whooping cough). We have previously determined the structure of TCT to be GlcNAc-1,6-anhydro-MurNAc-L-Ala-gamma-D-Glu-meso-A2pm-D-Ala, where MurNAc =
N-acetylmuramic acid and A2pm =
diaminopimelic acid. Purified TCT reproduces the respiratory cytopathology observed during
pertussis, including ciliostasis and extrusion of ciliated cells. We have tested structural analogs of TCT for their ability to reproduce native TCT toxicity in explanted hamster tracheal tissue and hamster trachea epithelial (HTE) cell cultures. Other investigators have evaluated many of these analogs, which are muramyl or desmuramyl
peptides, for muramyl
peptide activities such as immunopotentiation, induction of slow-wave sleep, and pyrogenicity. Four desmuramyl
peptides were produced in our laboratory from B.
pertussis peptidoglycan or by chemical synthesis, including unusual
peptides containing
alpha-aminopimelic acid in place of A2pm. Based on the relative ability of compounds to inhibit
DNA synthesis in HTE cells, truncated analogs lacking A2pm entirely or lacking only the side-chain
amine or carboxyl group of A2pm were less active than TCT by
a factor of at least 1000. All active analogs included a native or near-native
peptide moiety, independent of the presence, absence, or substitution of the
sugar moiety. We conclude that the structural requirements for TCT toxicity differ considerably from those for most other muramyl
peptide activities, in that the
disaccharide moiety is irrelevant for toxicity and both the free amino and carboxyl groups of the A2pm side chain are required for activity.