Tyrosine-Phosphorylated Bacterial Proteins: Trojan Horses for the Host Cell

For over a century, since the discovery by Roux and Yersin that sterile culture supernatants of Corynebacterium diphtheriae contained a potent toxin able to reproduce the lesions caused by diphtheria 1, most pathogenic bacteria have been considered to be microorganisms able to intoxicate local and distant tissues by secreting toxins in the extracellular medium. Recently, it has been shown that some bacteria inject toxic proteins directly into the cytoplasm of host cells using a specialized, needle-like 2 secretion apparatus (molecular syringe) known as a type III secretion system 3,4. A report in this issue by Ashai et al. 5 and reports from Haas et al. (Haas, R., personal communication), Segal et al. 6, and our own laboratory 7 now provide definitive evidence for the existence in Helicobacter pylori of a second type of molecular...