Structures of Type III Secretion System Needle Filaments
Among the Gram-negative bacterial secretion systems, type III secretion systems (T3SS) possess a unique extracellular molecular apparatus called the needle. This macromolecular protein assembly is a nanometre-size filament formed by the helical arrangemen
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Contents 1 Introduction.......................................................................................................................... 2 The T3SS Needle: Biological Functions ............................................................................ 3 Structures of Crystal and Soluble T3SS Needle Subunit Fragments................................. 4 Atomic Resolution Models of T3SS Needle Filaments ..................................................... 5 Structural Variability Between Salmonella and Shigella Needle Filaments ...................... 6 Towards an Assembly Mechanism of T3SS Needle Filaments ......................................... 7 Towards Functionalized T3SS Needles as Delivery Biotechnological Tools.................... 8 Concluding Remarks ........................................................................................................... References ..................................................................................................................................
Abstract Among the Gram-negative bacterial secretion systems, type III secretion systems (T3SS) possess a unique extracellular molecular apparatus called the needle. This macromolecular protein assembly is a nanometre-size filament formed by the helical arrangement of hundreds of copies of a single, small protein, which is highly conserved between T3SSs from animal to plant bacterial pathogens. The needle filament forms a hollow tube with a channel *20 Å in diameter that serves as a conduit for proteins secreted into the targeted host cell. In the past ten years, technical breakthroughs in biophysical techniques such as cryo-electron microscopy (cryo-EM) and solid-state NMR (SSNMR) spectroscopy have uncovered atomic resolution details about the T3SS needle assembly. Several high-resolution B. Habenstein (&) N. El Mammeri J. Tolchard G. Lamon A. Tawani M. Berbon A. Loquet (&) University of Bordeaux, CNRS, UMR 5248, European Institute of Chemistry and Biology, 2 rue Robert Escarpit, Pessac 33607, France e-mail: [email protected] A. Loquet e-mail: [email protected] Current Topics in Microbiology and Immunology https://doi.org/10.1007/82_2019_192 © Springer Nature Switzerland AG 2019
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structures of Salmonella typhimurium and Shigella flexneri T3SS needles have been reported demonstrating a common structural fold. These structural models have been used to explain the active role of the needle in transmitting the host-cell contact signal from the tip to the base of the T3SS through conformational changes as well as during the injection of effector proteins. In this chapter, we summarize the current knowledge about the structure and the role of the T3SS needle during T3SS assembly and effector secretion.
1 Introduction The type III secretion system (T3SS) is a complex virulence mechanism that has been reported for more than 20 Gram-negative bacteria, including Yersinia, Shigella and Salmonella species. These nanomachines lie at the heart of Gram-negative
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