RESUMO
The type III secretion system of Salmonella typhimurium directs the translocation of proteins into host cells. Evolutionarily related to the flagellar assembly machinery, this system is also present in other pathogenic bacteria, but its organization is unknown. Electron microscopy revealed supramolecular structures spanning the inner and outer membranes of flagellated and nonflagellated strains; such structures were not detected in strains carrying null mutations in components of the type III apparatus. Isolated structures were found to contain at least three proteins of this secretion system. Thus, the type III apparatus of S. typhimurium, and presumably other bacteria, exists as a supramolecular structure in the bacterial envelope.
Assuntos
Proteínas de Bactérias/análise , Proteínas de Bactérias/metabolismo , Proteínas de Membrana/análise , Proteínas de Membrana Transportadoras , Salmonella typhimurium/química , Salmonella typhimurium/ultraestrutura , Proteínas da Membrana Bacteriana Externa/análise , Proteínas de Bactérias/química , Proteínas de Bactérias/ultraestrutura , Membrana Celular/química , Membrana Celular/ultraestrutura , Centrifugação com Gradiente de Concentração , Substâncias Macromoleculares , Proteínas de Membrana/química , Proteínas de Membrana/ultraestrutura , Microscopia Eletrônica , Microscopia Imunoeletrônica , Porinas/análise , Salmonella typhimurium/metabolismoRESUMO
A number of bacterial pathogens have evolved sophisticated strategies to subvert host-cell signal-transduction pathways for their own benefit. These bacteria produce and export proteins capable of specific interactions with key mammalian cell regulatory molecules in order to derail the normal functions of the cells. In this study, we describe the identification of a modular effector protein secreted by the bacterial pathogen Salmonella typhimurium that is required for its full display of virulence. Sequence analysis revealed that a carboxy-terminal region of this protein, which we have termed SptP, is homologous to the catalytic domains of protein tyrosine phosphatases. Purified SptP protein efficiently dephosphorylated peptide substrates phosphorylated on tyrosine. An engineered mutant of SptP in which a critical Cys residue in the catalytic domain was changed to Ser was devoid of phosphatase activity, indicating a catalytic mechanism similar to that of other tyrosine phosphatases. In addition, an amino-terminal region of SptP exhibited sequence similarity to the ribosyltransferase exoenzyme S from Pseudomonas aeruginosa and the cytotoxin YopE from Yersinia spp. The modular nature of this effector protein may allow multiple interactions with host-cell signalling functions.
