Atomic model of the type III secretion system needle

• Published in: Nature (London) 2012-06, Vol.486 (7402), p.276-279
• Main Authors: Loquet, Antoine, Sgourakis, Nikolaos G., Gupta, Rashmi, Giller, Karin, Riedel, Dietmar, Goosmann, Christian, Griesinger, Christian, Kolbe, Michael, Baker, David, Becker, Stefan, Lange, Adam
• Format: Article
• Language: English
• Subjects: 631/1647/2204; 631/326/41/2536; Bacterial Secretion Systems; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; HeLa Cells; Humanities and Social Sciences; Humans; letter; Life Sciences; Microscopy, Electron; Models, Molecular; Molecular biophysics; multidisciplinary; Nuclear Magnetic Resonance, Biomolecular; Protein Structure, Secondary; Salmonella typhimurium; Salmonella typhimurium - chemistry; Science; Science (multidisciplinary); Shigella; Structure in molecular biology; Tridimensional structure
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature11079

The structure of the needle of the type III secretion system of Salmonella typhimurium , used to inject virulence proteins into host cells during infection, has been resolved by a combination of in vitro needle production, solid-state nuclear magnetic resonance, electron microscopy and Rosetta modelling at atomic resolution. Bacterial virulence injector structure The 'type-III' secretion system is used by many pathogenic bacteria to inject virulence proteins into host cells during infection. Using a combination of solid-state nuclear magnetic resonance imaging, electron microscopy and Rosetta modelling, the structure of the secretion needle at atomic resolution has now been resolved. The resulting atomic model reveals clearly defined supramolecular interfaces, an extended amino-terminal domain positioned on the surface of the needle, and a carboxy terminus pointing towards the lumen. Pathogenic bacteria using a type III secretion system (T3SS) 1 , 2 to manipulate host cells cause many different infections including Shigella dysentery, typhoid fever, enterohaemorrhagic colitis and bubonic plague. An essential part of the T3SS is a hollow needle-like protein filament through which effector proteins are injected into eukaryotic host cells 3 , 4 , 5 , 6 . Currently, the three-dimensional structure of the needle is unknown because it is not amenable to X-ray crystallography and solution NMR, as a result of its inherent non-crystallinity and insolubility. Cryo-electron microscopy combined with crystal or solution NMR subunit structures has recently provided a powerful hybrid approach for studying supramolecular assemblies 7 , 8 , 9 , 10 , 11 , 12 , resulting in low-resolution and medium-resolution models 13 , 14 , 15 , 16 , 17 . However, such approaches cannot deliver atomic details, especially of the crucial subunit–subunit interfaces, because of the limited cryo-electron microscopic resolution obtained in these studies. Here we report an alternative approach combining recombinant wild-type needle production, solid-state NMR, electron microscopy and Rosetta modelling to reveal the supramolecular interfaces and ultimately the complete atomic structure of the Salmonella typhimurium T3SS needle. We show that the 80-residue subunits form a right-handed helical assembly with roughly 11 subunits per two turns, similar to that of the flagellar filament of S. typhimurium . In contrast to established models of the needle in which the amino terminus of the protein subuni