@article{9748cee8c93d4750a211473c5e2dc7bd,
title = "Type 9 secretion system structures reveal a new protein transport mechanism",
abstract = "The type 9 secretion system (T9SS) is the protein export pathway of bacteria of the Gram-negative Fibrobacteres–Chlorobi–Bacteroidetes superphylum and is an essential determinant of pathogenicity in severe periodontal disease. The central element of the T9SS is a so-far uncharacterized protein-conducting translocon located in the bacterial outer membrane. Here, using cryo-electron microscopy, we provide structural evidence that the translocon is the T9SS protein SprA. SprA forms an extremely large (36-strand) single polypeptide transmembrane β-barrel. The barrel pore is capped on the extracellular end, but has a lateral opening to the external membrane surface. Structures of SprA bound to different components of the T9SS show that partner proteins control access to the lateral opening and to the periplasmic end of the pore. Our results identify a protein transporter with a distinctive architecture that uses an alternating access mechanism in which the two ends of the protein-conducting channel are open at different times.",
keywords = "Bacterial Secretion Systems/chemistry, Cryoelectron Microscopy, Flavobacterium/chemistry, Models, Molecular, Multiprotein Complexes/chemistry, Protein Binding, Protein Domains, Protein Structure, Secondary, Protein Transport",
author = "Frederic LAUBER and Deme, {Justin C} and Lea, {Susan M} and Berks, {Ben C}",
note = "Funding Information: Acknowledgements We thank M. McBride and Y. Zhu for providing reagents for the genetic manipulation of F. johnsoniae; A. Shrivastava and H. Berg for advice on measuring gliding motility; L. Lavis for supplying the Janelia Fluor 646 HaloTag ligand; S. Hickman for advice on fluorescence imaging; and O. Meacock and K. Foster for providing additional imaging facilities. We acknowledge the use of Central Oxford Structural Microscopy and Imaging Centre (COSMIC), the Oxford Micron Advanced Imaging Facility, and the Oxford Advanced Proteomics Facility. This work was supported by Wellcome Trust Investigator Awards 107929/Z/15/Z and 100298/Z/12/Z. COSMIC was supported by a Wellcome Trust Collaborative Award 201536/Z/16/Z, the Wolfson Foundation, a Royal Society Wolfson Refurbishment Grant, the John Fell Fund, and the EPA and Cephalosporin Trusts. Publisher Copyright: {\textcopyright} 2018, Springer Nature Limited. Copyright: Copyright 2019 Elsevier B.V., All rights reserved.",
year = "2018",
month = dec,
day = "6",
doi = "10.1038/s41586-018-0693-y",
language = "English",
volume = "564",
pages = "77--82",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7734",
}