Quantitative description of a contractile macromolecular machine

Contractile injection systems (CISs) [type VI secretion system (T6SS), phage tails, and tailocins] use a contractile sheath-rigid tube machinery to breach cell walls and lipid membranes. The structures of the pre- and postcontraction states of several CISs are known, but the mechanism of contraction remains poorly understood. Combining structural information of the end states of the 12-megadalton R-type pyocin sheath-tube complex with thermodynamic and force spectroscopy analyses and an original modeling procedure, we describe the mechanism of pyocin contraction. We show that this nanomachine has an activation energy of 160 kilocalories/mole (kcal/mol), and it releases 2160 kcal/mol of heat and develops a force greater than 500 piconewtons. Our combined approach provides a quantitative and experimental description of the membrane penetration process by a CIS.

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More Than Just a Spearhead: Diverse Functions of PAAR for Assembly and Delivery of Toxins of the Contractile Injection Systems

mSystems ◽

10.1128/msystems.01386-21 ◽

2021 ◽

Author(s):

Hao-Yu Zheng ◽

Liang Yang ◽

Tao Dong

Keyword(s):

Structural Component ◽

Secretion System ◽

Eukaryotic Cells ◽

Type Vi Secretion System ◽

Repeat Protein ◽

Rigid Tube ◽

Type Vi Secretion ◽

Outer Sheath ◽

Related Group

The type VI secretion system (T6SS) belongs to the evolutionarily related group of contractile injection systems that employ a contractile outer sheath to inject a rigid spear-like inner tube into target bacterial and eukaryotic cells. The tip of the rigid tube is often decorated by a PAAR-repeat protein as a key structural component.

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In vivo structures of an intact type VI secretion system revealed by electron cryotomography

10.1101/108233 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yi-Wei Chang ◽

Lee A. Rettberg ◽

Grant J. Jensen

Keyword(s):

Structural Information ◽

Cell Envelope ◽

Secretion System ◽

Tail Fiber ◽

Type Vi Secretion System ◽

Membrane Complex ◽

Type Vi Secretion ◽

Electron Cryotomography ◽

Structural Insights

SUMMARYThe type VI secretion system (T6SS) is a versatile molecular weapon used by many bacteria against eukaryotic hosts or prokaryotic competitors. It consists of a cytoplasmic bacteriophage tail-like structure anchored in the bacterial cell envelope via a cytoplasmic baseplate and a periplasmic membrane complex. Rapid contraction of the sheath in the bacteriophage tail-like structure propels an inner tube/spike complex through the target cell envelope to deliver effectors. While structures of purified contracted sheath and purified membrane complex have been solved, because sheaths contract upon cell lysis and purification, no structure is available for the extended sheath. Structural information about the baseplate is also lacking. Here we use electron cryotomography to directly visualize intact T6SS structures inside Myxococcus xanthus cells. Using sub-tomogram averaging, we resolve the structure of the extended sheath and membrane-associated components including the baseplate. Moreover, we identify novel extracellular bacteriophage tail fiber-like antennae. These results provide new structural insights into how the extended sheath prevents premature disassembly and how this sophisticated machine may recognize targets.

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