Type IX secretion: the generation of bacterial cell surface coatings involved in virulence, gliding motility and the degradation of complex biopolymers

5 years ago

Type IX secretion: the generation of bacterial cell surface coatings involved in virulence, gliding motility and the degradation of complex biopolymers

Michelle D. Glew, Paul D. Veith, Dhana G. Gorasia, Eric C. Reynolds

The Type IX secretion system (T9SS) is present in over 1000 sequenced species/strains of the Fibrobacteres-Chlorobi-Bacteroidetes superphylum. Proteins secreted by the T9SS have an N-terminal signal peptide for translocation across the inner membrane via the SEC translocon and a C-terminal signal for secretion across the outer membrane via the T9SS. Nineteen protein components of the T9SS have been identified including three, SigP, PorX and PorY that are involved in regulation. The inner membrane proteins PorL and PorM and the outer membrane proteins PorK and PorN interact and a complex comprising PorK and PorN forms a large ring structure of 50 nm in diameter. PorU, PorV, PorQ and PorZ form an attachment complex on the cell surface of the oral pathogen, Porphyromonas gingivalis. P. gingivalis T9SS substrates bind to PorV suggesting that after translocation PorV functions as a shuttle protein to deliver T9SS substrates to the attachment complex. The PorU component of the attachment complex is a novel Gram negative sortase which catalyses the cleavage of the C-terminal signal and conjugation of the protein substrates to lipopolysaccharide, anchoring them to the cell surface. This review presents an overview of the T9SS focusing on the function of T9SS substrates and machinery components. The Type IX secretion system is common in the Bacteroidetes phylum of Gram negative bacteria and is responsible for transporting substrate proteins across the outer membrane via a ‘translocation complex’ comprised of four core protein components. Some substrates then become part of the gliding machinery allowing locomotion, while other substrates are shuttled to the ‘attachment complex’ which cause the substrates to be tethered to the outer membrane to form functionally diverse cell surface coatings.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/mmi.13752