Structural snapshots of the Type 9 secretion system translocon
(2018) Midlands Molecular Microbiology Meeting — Location: Warwick, United Kingdom (13.September.2018)
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- Authors
Lauber, Frédéric 
- Abstract
- Background: The T9SS is a novel secretion system found in Gram-negative bacteria of the Fibrobacteres-Chlorobi-Bacteroidetes (FCB) superphylum. It is most notably associated with the human pathogen Porphyromonas gingivalis, the etiologic agent of chronic periodontitis, in which it is responsible for the secretion of the bacterium’s main virulence factors. T9SS substrates are secreted in a two-step process, using the general secretory (Sec) pathway to cross the inner membrane before being translocated across the outer membrane (OM) via the T9SS. While all core components of the T9SS have been identified, the identity of the protein(s) making up the OM translocon remains unknown. Aims: The purpose of this study was to identify and structurally characterize the T9SS translocon. Methods: A combination of fluorescence microscopy, biochemical (cryo-electron microscopy) and microbial methods were used in this work. Results: Here we show that the protein SprA is the T9SS translocon. We present two complexes of SprA bound to additional T9SS components and determine their structures using cryo-electron microscopy. SprA forms an unprecedentedly 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. Partner proteins control access to the lateral opening and to the periplasmic end of the pore. Conclusions: Our results uncover a protein secretion system with a distinctive architecture that operates a novel alternating access mechanism for translocation in which the two ends of the protein conducting channel are open at different times.
- Affiliations
Department of Biochemistry University of Oxford
Citations
Lauber, F. (2018). Structural snapshots of the Type 9 secretion system translocon. Midlands Molecular Microbiology Meeting, Warwick, United Kingdom. https://hdl.handle.net/2078.5/215268