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THE YERSINIA YSC-YOP ‘TYPE III’ WEAPONRY G.R. Cornelis, 2002. Nature Reviews

This article discusses the Yersinia bacteria's Type III secretion system, which allows them to inject proteins into host cells and manipulate cellular processes. The importance, mechanisms, and effects of this secretion system are explored, shedding light on the pathogenicity of Yersinia.

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THE YERSINIA YSC-YOP ‘TYPE III’ WEAPONRY G.R. Cornelis, 2002. Nature Reviews

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  1. THE YERSINIA YSC-YOP ‘TYPE III’ WEAPONRY G.R. Cornelis, 2002. Nature Reviews in Molecular Cell Biology 3: 742-752.

  2. TYPE III SECRETION • What is it? • Why is it important? • Who does it?

  3. TYPE III SECRETION • Bacteria inject proteins across cellular membranes into the host cell cytosol that have complex effects on intracellular systems. • Type III secretion systems (TTSS) are found in a variety of animals, plants, and insects but the evolution is unclear. • TTSS are often plasmid-encoded.

  4. Yersinia TTSS • Yops – Yersinia outer proteins • Ysc – Yop secretion apparatus • Effectors – Yops that enter the host cell and alter host cell functioning. • Injectisome – bacterial organelle that secretes the effector proteins into the host cell.

  5. Yersinia TTSS Overview • Yersinia adhere to cell surface and deliver Yops into host cell cytosol with injectisome. • Yops functions: • 1) cytoskeletal effects interfere with phagocytosis. • 2) inhibit production of cytokines, chemokines, and adhesion molecules. • Yersinia are better able to survive and multiply in lymphoid tissues by using the TTSS.

  6. Yops • Translocator Yops: • YopB, YopD, LcrV form the pore for delivery. • Effector Yops: • YopH, YopE, YopT, YpkA/YopO – cytoskeletal disturbances, inhibition of phagocytosis. • YopP – downregulation of inflammatory response. • YopM – function uncertain.

  7. INJECTISOME • Basal body with protein pump (YscN) and a central pore (YscC). • Needle-like projection (YscF) for Yops delivery. From: Cornelis, G.R., 2002. Yersinia Type III secretion: send in the effectors. Journal of Cell Biology 158 (3): 401-408.

  8. INJECTISOME • Translocator YopB, YopD, LcrV are required to form pores for cell delivery. • Some Yops require chaperone proteins. • YopN, TyeA, LcrG plug the injectisome channel before Yops delivery to cell. • Cell adhesion required for injectisome function.

  9. INJECTISOME • Does the injectisome ‘needle’ pierce the host cell membrane, retract, or break down? • Maybe translocator Yops destabilize host cell membranes after adhesion to allow piercing? • Once the pore is formed, even non-effector proteins can be delivered to the host cell!

  10. From: Cornelis, G.R., 2002. Yersinia Type III secretion: send in the effectors. Journal of Cell Biology 158 (3): 401-408.

  11. YOPS EFFECTS • Phagocyte paralysis • Reduction in pro-inflammatory response • Inhibition of lymphocyte proliferation

  12. PHAGOCYTE PARALYSIS • Synergistic effects of Yops H, E, T, and O. • YopH – a phosphotyrosine phosphotase (PTPase) • Dephosphorylates focal adhesion protein p130. • Dephosphoylates scaffolding proteins SKAP-HOM. • Suppresses oxidative burst in macrophages. • Reduces calcium signals needed for phagocytosis.

  13. PHAGOCYTE PARALYSIS • YopE – a GTPase activating protein (GAP) that hydrolyzes Rho, Rac, Cdc42 to ‘off’ position. • YopT – a cysteine protease that inactivates Rho, Rac, Cdc42 by cleaving from plasma membrane. • YpkA/YopO – an autophosphorylating serine/threonine kinase that inhibits Rho and Rac by an unknown mechanism.

  14. From: Cornelis, G.R., 2002. Yersinia Type III secretion: send in the effectors. Journal of Cell Biology 158 (3): 401-408.

  15. INHIBITING INFLAMMATION • YopP – possibly a SUMO protease. • Inhibits the IKKB that would phosphorylate IKB to release inhibition of NF-KB. Because NF-KB is inhibited, PMN recruitment decreases due to: • Decreased TNF release by macrophages. • Decreased IL-8 release from epithelial and endothelial cells. • Decreased ICAM and E-selectin adhesion molecule expression on endothelial cells.

  16. INHIBITING INFLAMMATION • Other YopP effects: • Inhibition of MAPK kinases that keep the CREB transcription factor from being activated. • Induction of macrophage apoptosis by cleavage of the Bcl-2 protein Bid, release of cytochrome c from mitochondria, and activation of caspases.

  17. INHIBITING INFLAMMATION • YopH – in addition to antiphagocytic activities: • Inhibition of the PI3K/Akt pathway, causing: • Reduced MCP1 synthesis that is needed to recruit macrophages to lymph nodes. • Reduced T cell ability for cytokine production. • Reduced B cell ability to upregulate surface costimulatory molecules such as CD86.

  18. From: Cornelis, G.R., 2002. Yersinia Type III secretion: send in the effectors. Journal of Cell Biology 158 (3): 401-408.

  19. MYSTERIOUS YOPS • YopM – important virulence factor in mice. • Subunits form a hollow cylinder. • Uses a vesicle associated pathway to migrate to cell nucleus and inhibit transcription of genes involved in cell growth and proliferation. • LcrV – in addition to translocation of Yops: • Promotes IL-10 production that suppresses TNF production in macrophages. • IL-10 deficient mice are more resistant to Yersinia infection but mechanisms are difficult to study.

  20. From: Cornelis, G.R., 2002. Yersinia Type III secretion: send in the effectors. Journal of Cell Biology 158 (3): 401-408.

  21. CONCLUSIONS • Translocator Yops – B, D, LcrV. • Effector Yops – Yop H, E, T, O, P, M. • Yersinia Ysc-Yop TTSS has complex effects: • Inhibition of phagocytosis. • Reduced recruitment of PMNs and macrophages. • Inhibition of lymphocyte proliferation.

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