The zeta toxins are a family of proteins that are normally present within various pathogenic bacteria and can mysteriously trigger suicide when the cells undergo stress. A team led by Dr. Anton Meinhart at the Max Planck Institute for Medical Research in Heidelberg has now found the mechanism underlying this programmed bacterial cell death. The team’s paper, published in PLoS Biology, reports that zeta toxins convert a compound required for bacterial cell wall synthesis into a poison that kills bacteria from within. In the future, it may be possible to hijack this mechanism for defense against bacteria and to design drugs that mimic these toxins. Most bacteria harbor toxin-antitoxin (TA) systems, in which a bacterial toxin lies dormant under normal conditions, prevented from being active by its antitoxin counterpart. As long as the antitoxin is present, the bacterium can continue to exist and is not affected by the TA system. Under conditions of stress, however, the antitoxin is degraded, freeing the toxin to attack its host from within. Although the family of zeta toxins was discovered almost 20 years ago, their deadly mechanism has been enigmatic until now. The first author on the paper, Dr. Hannes Mutschler, and his colleagues studied the molecular mechanism of action of the zeta toxin PezT from the PezAT (Pneumococcal epsilon zeta Antitoxin Toxin) system using the model bacterium Escherichia coli. The PezAT system is found in the major human pathogen Streptococcus pneumoniae - a bacterium that causes serious infections such as pneumonia, septicemia, and meningitis. Bacterial cells in which PezT was activated showed symptoms of poisoning similar to the effects of penicillin. This involved first stalling in the middle of their division stage, and later the intersection zone between the two cell bodies burst and the cells died.
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