4d3e
Tetramer of IpaD, modified from 2J0O, fitted into negative stain electron microscopy reconstruction of the wild type tip complex from the type III secretion system of Shigella flexneri
Structural highlights
FunctionIPAD_SHIFL Required for bacterial invasion of host cells. Controls IpaB and IpaC secretion, and the efficiency with which they are physically inserted into target cell membranes. These proteins are exported via TTSS to form a pore in the host membrane that allows the translocation of the other effectors into the host cytoplasm. Along with IpaB, is essential for both blocking secretion through the Mxi/Spa translocon in the absence of a secretion-inducing signal, and for controlling the level of secretion in the presence of this signal.[1] [2] Publication Abstract from PubMedType III secretion systems are found in many Gram-negative bacteria. They are activated by contact with eukaryotic cells and inject virulence proteins inside them. Host cell detection requires a protein complex located at the tip of the device's external injection needle. The Shigella tip complex (TC) is composed of IpaD, a hydrophilic protein, and IpaB, a hydrophobic protein, which later forms part of the injection pore in the host membrane. Here we used labelling and crosslinking methods to show that TCs from a DeltaipaB strain contain five IpaD subunits while the TCs from wild-type can also contain one IpaB and four IpaD subunits. Electron microscopy followed by single particle and helical image analysis was used to reconstruct three-dimensional images of TCs at approximately 20 A resolution. Docking of an IpaD crystal structure, constrained by the crosslinks observed, reveals that TC organisation is different from that of all previously proposed models. Our findings suggest new mechanisms for TC assembly and function. The TC is the only site within these secretion systems targeted by disease-protecting antibodies. By suggesting how these act, our work will allow improvement of prophylactic and therapeutic strategies. Three-dimensional electron microscopy reconstruction and cysteine-mediated crosslinking provide a model of the type III secretion system needle tip complex.,Cheung M, Shen DK, Makino F, Kato T, Roehrich AD, Martinez-Argudo I, Walker ML, Murillo I, Liu X, Pain M, Brown J, Frazer G, Mantell J, Mina P, Todd T, Sessions RB, Namba K, Blocker AJ Mol Microbiol. 2014 Oct 29. doi: 10.1111/mmi.12843. PMID:25353930[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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