Atomic Structure of Type VI Contractile Sheath from Pseudomonas aeruginosa

Osman Salih,Shaoda He,Sara Planamente,Lasse Stach,James T Macdonald,Eleni Manoli,Sjors H.W Scheres,Alain Filloux,Paul S Freemont

doi:10.1016/j.str.2017.12.005

Osman Salih, Shaoda He + Show 7 more

Open Access

https://doi.org/10.1016/j.str.2017.12.005

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Abstract

SummaryPseudomonas aeruginosa has three type VI secretion systems (T6SSs), H1-, H2-, and H3-T6SS, each belonging to a distinct group. The two T6SS components, TssB/VipA and TssC/VipB, assemble to form tubules that conserve structural/functional homology with tail sheaths of contractile bacteriophages and pyocins. Here, we used cryoelectron microscopy to solve the structure of the H1-T6SS P. aeruginosa TssB1C1 sheath at 3.3 Å resolution. Our structure allowed us to resolve some features of the T6SS sheath that were not resolved in the Vibrio cholerae VipAB and Francisella tularensis IglAB structures. Comparison with sheath structures from other contractile machines, including T4 phage and R-type pyocins, provides a better understanding of how these systems have conserved similar functions/mechanisms despite evolution. We used the P. aeruginosa R2 pyocin as a structural template to build an atomic model of the TssB1C1 sheath in its extended conformation, allowing us to propose a coiled-spring-like mechanism for T6SS sheath contraction.

Highlights

The type VI secretion system (T6SS) is a contractile injection machine widely distributed among Gram-negative bacteria
Cryo-EM Structure of the TssB1C1 Sheath of Pseudomonas aeruginosa P. aeruginosa TssB1 and TssC1 proteins produced in Escherichia coli spontaneously assemble (1:1 stoichiometry) to form tubes (Lossi et al, 2013)
This is further supported by negative-stain EM data showing that TssB1C1 sheaths produced in the native host P. aeruginosa have 12-fold symmetry (Figure S1B)

Summary

Graphical Abstract

Salih et al present the atomic structure of a contracted sheath of a type VI secretion system, revealing unique features. Comparison with other systems suggests a conserved sheath contraction mechanism among T6SS groups. The authors suggest a coiled-spring-like mechanism for T6SS sheath contraction. Highlights d We solved a T6SS sheath structure from Pseudomonas aeruginosa (group 3 T6SSi). D Comparisons between T6SS groups suggest a conserved sheath contraction mechanism d Extended-state model led to proposal of a spring-like sheath contraction mechanism. 2018, Structure 26, 329–336 February 6, 2018 a 2017 The Author(s).

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