Type VI secretion delivers bacteriolytic effectors to target cells

Alistair B. Russel, et al. Nature. 475, 343-347(2011)

Speaker: Shih Fang Huang (黃詩方)                            Time: 15:00~16:00, Nov. 9, 2011

Commentator: Dr. Jiunn-Jong Wu (吳俊忠博士) Place: Room 601

Abstract:

The type VI secretion system (T6SS), a complex and widely distributed protein export machine, is one of the tools for the bacteria to adapt to and compete in the environment. In a polymicrobial infection, the gram-negative bacteria often compete with each other for accessing to a nutrient-rich host tissue by targeting their effectors (toxins or enzymes). Factors, such as T6SS, that influence the relative fitness of these organisms are thus likely to have an impact on disease outcome. However, the mechanisms by which the effectors are delivered via the T6S apparatus and the functions of the effectors within recipient cells remain elusive. In 2010, three type T6S exported proteins, Tse1–3, have been identified in P. aeruginosa. It has been shown that Tse2 is the toxin component of a toxin-immunity system, which arrests the growth of a variety of prokaryocytes by an unknown mechanism. Further in this paper, the authors indicated that 1) Tse1 and Tse3 are lytic enzymes that degrade peptidoglycan via amidase and muramidase activities; 2) Tse1 and Tse3 function as lytic antibacterial effectors, rather than accessory enzymes of the T6S apparatus assembly, that depend upon T6SS to breach the outer membrane of a gram-negative bacterial cell for them to enter the periplasm; 3) the bacterium synthesizes the immunity proteins,T6S immunity 1 and 3 (Tsi1 and Tsi3), that specifically inactivate Tse1 and Tse3. In conclusion, the authors proposed a model for T6SS-catalysed translocation of effectors to the periplasm of the recipient bacteria. This model provides a mechanistic framework for understanding the structure and function of this complex secretion system.

References:

1.      Hood R. D. et al. A type VI secretion system of Pseudomonas aeruginosa targets a toxin to bacteria. Cell Host Microbe 7, 25–37 (2010)

2.      Filloux A. et al. The bacterial type VI secretion machine: yet another player for protein transport across membranes. Microbiology 154, 1570–1583 (2008)

3.      Russel A. B. et al. Type VI secretion delivers bacteriolytic effectors to target cells. Nature. 475, 343-347 (2011)