Journal
EMBO JOURNAL
Volume 37, Issue 4, Pages -Publisher
WILEY
DOI: 10.15252/embj.201797103
Keywords
baseplate; contractile tails; cryo-electron microscopy; sheath; Type VI secretion system
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Funding
- Swiss National Science Foundation (SNSF) [31003A_159525]
- University of Basel
- SNSF NCCR TransCure
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The bacterial Type VI secretion system (T6SS) assembles from three major parts: a membrane complex that spans inner and outer membranes, a baseplate, and a sheath-tube polymer. The baseplate assembles around a tip complex with associated effectors and connects to the membrane complex by TssK. The baseplate assembly initiates sheath-tube polymerization, which in some organisms requires TssA. Here, we analyzed both ends of isolated non-contractile Vibrio cholerae sheaths by cryo-electron microscopy. Our analysis suggests that the baseplate, solved to an average 8.0 angstrom resolution, is composed of six subunits of TssE/F-2/G and the baseplate periphery is decorated by six TssK trimers. The VgrG/PAAR tip complex in the center of the baseplate is surrounded by a cavity, which may accommodate up to similar to 450 kDa of effector proteins. The distal end of the sheath, resolved to an average 7.5 angstrom resolution, shows sixfold symmetry; however, its protein composition is unclear. Our structures provide an important step toward an atomic model of the complete T6SS assembly.
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