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Tracheal cytotoxin structural requirements for respiratory epithelial damage in pertussis
K E Luker1, A N Tyler, G R Marshall
1Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093, USA.
Abstract:
The respiratory epithelial pathology of pertussis (whooping cough) can be reproduced by tracheal cytotoxin (TCT), a disaccharide-tetrapeptide released by Bordetella pertussis. TCT is a muramyl peptide, a class of peptidoglycan-derived compounds which have many biological activities including adjuvanticity, somnogenicity, pyrogenicity, and cytotoxicity. The structural requirements for muramyl peptides to produce some of these biological effects have been partially characterized. Using in vitro assays with respiratory epithelial cells and tissue, we have previously determined that the disaccharide moiety of TCT is not involved in toxicity and that the side-chain functional groups of diaminopimelic acid (A2pm) are crucial for toxicity. In this study, we determine the importance of every amino acid, functional group and chiral centre in the peptide portion of TCT. Although lactyl tetrapeptides are the most toxic of the TCT fragments, producing dose-response curves identical to TCT, the smallest analogues of TCT which are active in our assay are of the form X-gamma-(D)-Glu-meso-A2pm, where X may be an amino acid or a blocking group. Within this active substructure, main-chain chirality and all functional groups are essential for toxicity. This definition of the core region of TCT indicates that the TCT interaction site is unlike almost all other muramyl peptide interaction sites for which structure-activity data are available.
Insights
Tracheal cytotoxin (TCT) from Bordetella pertussis causes whooping cough pathology. Its toxicity relies on specific amino acids and chirality in its peptide structure, not the disaccharide.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Pertussis (whooping cough) involves respiratory epithelial damage.
- Tracheal cytotoxin (TCT), released by Bordetella pertussis, reproduces this pathology.
- TCT is a muramyl peptide with various biological activities, including cytotoxicity.
Purpose of the Study:
- To determine the specific structural requirements for TCT's toxicity.
- To identify the essential components within the peptide portion of TCT responsible for its cytotoxic effects.
- To compare the TCT interaction site with other known muramyl peptide interaction sites.
Main Methods:
- In vitro assays using respiratory epithelial cells and tissue.
- Systematic modification and testing of amino acids, functional groups, and chiral centers in the TCT peptide portion.
- Analysis of structure-activity relationships for TCT analogues.
Main Results:
- The disaccharide moiety of TCT is not essential for toxicity.
- Specific functional groups and main-chain chirality within the peptide portion are crucial for TCT toxicity.
- The smallest toxic TCT analogues identified have the structure X-gamma-(D)-Glu-meso-A2pm.
Conclusions:
- The core toxic region of TCT is defined by its peptide structure, specifically the gamma-(D)-Glu-meso-A2pm substructure.
- The TCT interaction site appears unique compared to other characterized muramyl peptide interaction sites.
- Understanding TCT's structure-activity relationship is key to understanding pertussis pathogenesis.