Molecular Characterization and Assembly of the Needle Complex of the Salmonella typhimurium Type III Protein Secretion System

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-08, Vol.97 (18), p.10225-10230
• Main Authors: Kubori, T, Sukhan, A, Aizawa, S I, Galán, J E
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animal cells; Antibodies; Antigens, Bacterial; Bacteria; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological Sciences; Cell Membrane - physiology; Cell Membrane - ultrastructure; Gels; Genetic mutation; InvG protein; Medical syringes; Membrane Transport Proteins; Microbiology; Molecular Sequence Data; needle complex; Plasmids; PrgH protein; PrgK protein; Protein secretion; Proteins; Salmonella; Salmonella typhimurium; Salmonella typhimurium - genetics; Salmonella typhimurium - pathogenicity; Salmonella typhimurium - physiology; Salmonella typhimurium - ultrastructure; Secretion; Sequence Alignment; Sequence Homology, Amino Acid; type III protein secretion system; Virulence - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.170128997

Many bacterial pathogens of plants and animals have evolved a specialized protein-secretion system termed type III to deliver bacterial proteins into host cells. These proteins stimulate or interfere with host cellular functions for the pathogen's benefit. The Salmonella typhimurium pathogenicity island 1 encodes one of these systems that mediates this bacterium's ability to enter nonphagocytic cells. Several components of this type III secretion system are organized in a supramolecular structure termed the needle complex. This structure is made of discrete substructures including a base that spans both membranes and a needle-like projection that extends outward from the bacterial surface. We demonstrate here that the type III secretion export apparatus is required for the assembly of the needle substructure but is dispensable for the assembly of the base. We show that the length of the needle segment is determined by the type III secretion associated protein InvJ. We report that InvG, PrgH, and PrgK constitute the base and that PrgI is the main component of the needle of the type III secretion complex. PrgI homologs are present in type III secretion systems from bacteria pathogenic for animals but are absent from bacteria pathogenic for plants. We hypothesize that the needle component may establish the specificity of type III secretion systems in delivering proteins into either plant or animal cells.