Rhs toxins

Rhs toxins belong to the polymorphic toxin category of bacterial exotoxins.[1] Rhs proteins are widespread and can be produced by both Gram-negative and Gram-positive bacteria.[2] Rhs toxins are very large proteins of usually more than 1,500 aminoacids with variable C-terminal toxic domains. Their toxic activity can either target eukaryotes or other bacteria.

Domain architecture

In their large N-terminal region, Rhs toxins comprise RHS/YD repeats in various number (PF05593) (RHS meaning Rearrangement Hot Spot) [3] and another "RHS-repeats associated core" domain (PF03527). In contrast, their C-terminal regions are shorter and harbor highly variable C-terminal domains including many domains with a predicted nuclease activity.[2]

Function

Anti-eukaryotic activity

These toxins encompass Rhs toxins of insect pathogens with an activity against insects.[4] This group also include Rhs toxins with an activity against human phagocytic cells that contribute to pathogenesis of Pseudomonas aeruginosa.[5]

Anti-bacterial activity

A role in inter-bacterial competition has been demonstrated for the plant pathogen Dickeya dadantii and for the human pathogen Escherichia coli.[6][7]

When a polymorphic toxin with anti-bacterial activity is produced by a bacterial strain, this strain is protected by a specific immunity protein encoded by a gene immediately downstream of the toxin gene.[1]

Delivery

Some Rhs toxins such as the previously mentioned system in Dickeya dadantii appear to be dependent on the type VI secretion system for delivery into neighbouring cells.[6] PAAR domain toxins such as Rhs appear to form the sharp tip of the type VI secretion system being attached to the VgrG of the secretion apparatus.[8] The C-terminal toxins of Rhs may vary to diversify the antimicrobial activity of the type VI secretion system.[7]

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References
  1. Jamet A, Nassif X (May 2015). "New players in the toxin field: polymorphic toxin systems in bacteria". mBio. 6 (3): e00285-15. doi:10.1128/mBio.00285-15. PMC 4436062. PMID 25944858.
  2. Zhang D, de Souza RF, Anantharaman V, Iyer LM, Aravind L (June 2012). "Polymorphic toxin systems: Comprehensive characterization of trafficking modes, processing, mechanisms of action, immunity and ecology using comparative genomics". Biology Direct. 7: 18. doi:10.1186/1745-6150-7-18. PMC 3482391. PMID 22731697.
  3. Hill CW, Sandt CH, Vlazny DA (June 1994). "Rhs elements of Escherichia coli: a family of genetic composites each encoding a large mosaic protein". Molecular Microbiology. 12 (6): 865–71. doi:10.1111/j.1365-2958.1994.tb01074.x. PMID 7934896.
  4. Busby JN, Panjikar S, Landsberg MJ, Hurst MR, Lott JS (September 2013). "The BC component of ABC toxins is an RHS-repeat-containing protein encapsulation device" (PDF). Nature. 501 (7468): 547–50. doi:10.1038/nature12465. PMID 23913273.
  5. Kung VL, Khare S, Stehlik C, Bacon EM, Hughes AJ, Hauser AR (January 2012). "An rhs gene of Pseudomonas aeruginosa encodes a virulence protein that activates the inflammasome". Proceedings of the National Academy of Sciences of the United States of America. 109 (4): 1275–80. doi:10.1073/pnas.1109285109. PMC 3268321. PMID 22232685.
  6. Koskiniemi S, Lamoureux JG, Nikolakakis KC, t'Kint de Roodenbeke C, Kaplan MD, Low DA, Hayes CS (April 2013). "Rhs proteins from diverse bacteria mediate intercellular competition". Proceedings of the National Academy of Sciences of the United States of America. 110 (17): 7032–7. doi:10.1073/pnas.1300627110. PMC 3637788. PMID 23572593.
  7. Ma J, Sun M, Dong W, Pan Z, Lu C, Yao H (January 2017). "PAAR-Rhs proteins harbor various C-terminal toxins to diversify the antibacterial pathways of type VI secretion systems". Environmental Microbiology. 19 (1): 345–360. doi:10.1111/1462-2920.13621. PMID 27871130.
  8. Shneider MM, Buth SA, Ho BT, Basler M, Mekalanos JJ, Leiman PG (August 2013). "PAAR-repeat proteins sharpen and diversify the type VI secretion system spike" (PDF). Nature. 500 (7462): 350–353. doi:10.1038/nature12453. PMC 3792578. PMID 23925114.
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