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==Discovery==
==Discovery==
The first vapBC system to be characterised was found in ''[[Salmonella dublin]]'' strain G19 in 1992.<ref name="Pull92">{{cite journal|last=Pullinger|first=GD|coauthors=Lax, AJ|title=A Salmonella dublin virulence plasmid locus that affects bacterial growth under nutrient-limited conditions.|journal=Molecular microbiology|date=1992 Jun|volume=6|issue=12|pages=1631-43|pmid=1495391|accessdate=11 May 2011}}</ref> It was characterised as a system for coordinating the replication of a virulence plasmid with cell division. The two components of this plasmidic system were originally named ''vagC'' and ''vagD'' (virulence-associated gene) for the toxin and antitoxin genes respectively. ''vagC'' was predicted to encode a 12[[Atomic mass unit|kDa]] polypeptide, while ''vagD'' encoded a smaller 10kDa protein.<ref name="Pull92" /> Their [[open reading frame]]s were found to overlap by a single [[nucleotide]]; suggesting they were translated together, and at a constant [[Mole (unit)|molar]] ratio.<ref>{{cite journal|last=Das|first=A|coauthors=Yanofsky, C|title=Restoration of a translational stop-start overlap reinstates translational coupling in a mutant trpB'-trpA gene pair of the Escherichia coli tryptophan operon.|journal=Nucleic acids research|date=1989 Nov 25|volume=17|issue=22|pages=9333-40|pmid=2685759|accessdate=13 May 2011}}</ref>
Following the discoveries of two other type II toxin-antitoxin systems,<ref>{{cite journal|last=Ogura|first=T|coauthors=Hiraga, S|title=Mini-F plasmid genes that couple host cell division to plasmid proliferation.|journal=Proceedings of the National Academy of Sciences of the United States of America|date=1983 Aug|volume=80|issue=15|pages=4784-8|pmid=6308648|accessdate=13 May 2011}}</ref><ref>{{cite journal|last=Bravo|first=A|coauthors=de Torrontegui, G, Díaz, R|title=Identification of components of a new stability system of plasmid R1, ParD, that is close to the origin of replication of this plasmid.|journal=Molecular & general genetics : MGG|date=1987 Nov|volume=210|issue=1|pages=101-10|pmid=3323833|accessdate=13 May 2011}}</ref> the first vapBC system to be characterised was found in ''[[Salmonella dublin]]'' strain G19 in 1992.<ref name="Pull92">{{cite journal|last=Pullinger|first=GD|coauthors=Lax, AJ|title=A Salmonella dublin virulence plasmid locus that affects bacterial growth under nutrient-limited conditions.|journal=Molecular microbiology|date=1992 Jun|volume=6|issue=12|pages=1631-43|pmid=1495391|accessdate=11 May 2011}}</ref> It was characterised as a system for coordinating the replication of a virulence plasmid with cell division. The two components of this plasmidic system were originally named ''vagC'' and ''vagD'' (virulence-associated gene) for the toxin and antitoxin genes respectively. ''vagC'' was predicted to encode a 12[[Atomic mass unit|kDa]] polypeptide, while ''vagD'' encoded a smaller 10kDa protein.<ref name="Pull92" /> Their [[open reading frame]]s were found to overlap by a single [[nucleotide]]; suggesting they were translated together, and at a constant [[Mole (unit)|molar]] ratio.<ref>{{cite journal|last=Das|first=A|coauthors=Yanofsky, C|title=Restoration of a translational stop-start overlap reinstates translational coupling in a mutant trpB'-trpA gene pair of the Escherichia coli tryptophan operon.|journal=Nucleic acids research|date=1989 Nov 25|volume=17|issue=22|pages=9333-40|pmid=2685759|accessdate=13 May 2011}}</ref>


==Distribution==
==Distribution==

Revision as of 15:28, 13 May 2011

Crystallographic tertiary structure of a VapC toxin PIN domain.

vapBC (virulence associated proteins B and C) is the largest family of type II toxin-antitoxin system loci in prokaryotes.[1] vapBC operons consist of a VapC toxin, a PilT N-terminus (PIN) domain, and a VapB antitoxin.[2] The toxins in these families are thought to perform RNA cleavage, which is inhibited by the co-expression of the antitoxin, in a manner analogous to a 'poison and antidote' system. First discovered in 1992, vapBC loci are now thought make up around 37% of all type II toxin-antitoxin systems.[3]

Discovery

Following the discoveries of two other type II toxin-antitoxin systems,[4][5] the first vapBC system to be characterised was found in Salmonella dublin strain G19 in 1992.[6] It was characterised as a system for coordinating the replication of a virulence plasmid with cell division. The two components of this plasmidic system were originally named vagC and vagD (virulence-associated gene) for the toxin and antitoxin genes respectively. vagC was predicted to encode a 12kDa polypeptide, while vagD encoded a smaller 10kDa protein.[6] Their open reading frames were found to overlap by a single nucleotide; suggesting they were translated together, and at a constant molar ratio.[7]

Distribution

vapBC operons have been found in distantly related prokaryotes, including the pathogens Leptospira interrogans,[8] Mycobacterium tuberculosis[9] and Piscirickettsia salmonis.[10] The loci have been described as "surprisingly abundant, especially in Archaea"[11] and made up 37% of all TA families identified by one bioinformatics search.[3]

Bioinformatics searches have discovered vapBC homologues on both chromosomes and plasmids, and often in high copy number per cell. They are less common, however, in firmicutes and cyanobacteria.[3] Genomes with high numbers of vapBC loci include: M. tuberculosis with 45 predicted loci and Sinorhizobium meliloti with 21.[9]

Function(s)

VapC toxins, specifically the PIN domains, act as ribonucleases in cleaving RNA molecules, thereby reducing the rate of translation.[9][12] In the bacteria Shigella flexneri and Salmonella enterica, VapC toxins have been shown to perform specific cleavage of a tRNA, but in other bacteria the RNA cleavage may be less-specific.[13]

VapC is strongly inhibited by direct protein interaction with VapB, its cognate antitoxin. The toxin-antitoxin complex is thought to autoregulate its own operon, repressing transcription of both components through a DNA-binding domain in VapB.[14]

In some organisms, vapBC loci have been assigned other potential functions. In the hyperthermophilic archaean Sulfolobus solfataricus, for example, a vapBC gene cassette is though to regulate heat shock response.[2]

See also

References

  1. ^ Robson, Jennifer (17 July 2009). "The vapBC Operon from Mycobacterium smegmatis Is An Autoregulated Toxin–Antitoxin Module That Controls Growth via Inhibition of Translation". Journal of Molecular Biology. 390 (3): 353–367. doi:10.1016/j.jmb.2009.05.006. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ a b Cooper, CR (2009 Feb). "Role of vapBC toxin-antitoxin loci in the thermal stress response of Sulfolobus solfataricus". Biochemical Society transactions. 37 (Pt 1): 123–6. PMID 19143615. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  3. ^ a b c Sevin, Emeric W (1 January 2007). "RASTA-Bacteria: a web-based tool for identifying toxin-antitoxin loci in prokaryotes". Genome Biology. 8 (8): R155. doi:10.1186/gb-2007-8-8-r155. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)
  4. ^ Ogura, T (1983 Aug). "Mini-F plasmid genes that couple host cell division to plasmid proliferation". Proceedings of the National Academy of Sciences of the United States of America. 80 (15): 4784–8. PMID 6308648. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Bravo, A (1987 Nov). "Identification of components of a new stability system of plasmid R1, ParD, that is close to the origin of replication of this plasmid". Molecular & general genetics : MGG. 210 (1): 101–10. PMID 3323833. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ a b Pullinger, GD (1992 Jun). "A Salmonella dublin virulence plasmid locus that affects bacterial growth under nutrient-limited conditions". Molecular microbiology. 6 (12): 1631–43. PMID 1495391. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  7. ^ Das, A (1989 Nov 25). "Restoration of a translational stop-start overlap reinstates translational coupling in a mutant trpB'-trpA gene pair of the Escherichia coli tryptophan operon". Nucleic acids research. 17 (22): 9333–40. PMID 2685759. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Zhang, YX (2004 Jun). "Characterization of a novel toxin-antitoxin module, VapBC, encoded by Leptospira interrogans chromosome". Cell research. 14 (3): 208–16. PMID 15225414. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  9. ^ a b c Arcus, V. L. (29 October 2010). "The PIN-domain ribonucleases and the prokaryotic VapBC toxin-antitoxin array". Protein Engineering Design and Selection. 24 (1–2): 33–40. doi:10.1093/protein/gzq081. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Gómez, FA (2011 Apr). "Characterization of a functional toxin-antitoxin module in the genome of the fish pathogen Piscirickettsia salmonis". FEMS microbiology letters. 317 (1): 83–92. PMID 21241361. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ Gerdes, K (2005 May). "Prokaryotic toxin-antitoxin stress response loci". Nature reviews. Microbiology. 3 (5): 371–82. PMID 15864262. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Van Melderen, Laurence (1 December 2010). "Toxin–antitoxin systems: why so many, what for?". Current Opinion in Microbiology. 13 (6): 781–785. doi:10.1016/j.mib.2010.10.006. {{cite journal}}: |access-date= requires |url= (help)
  13. ^ Winther, K. S. (18 April 2011). "Enteric virulence associated protein VapC inhibits translation by cleavage of initiator tRNA". Proceedings of the National Academy of Sciences. 108 (18): 7403–7407. doi:doi:10.1073/pnas.1019587108. {{cite journal}}: |access-date= requires |url= (help); Check |doi= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  14. ^ Miallau, L. (4 November 2008). "Structure and Proposed Activity of a Member of the VapBC Family of Toxin-Antitoxin Systems: VapBC-5 FROM MYCOBACTERIUM TUBERCULOSIS". Journal of Biological Chemistry. 284 (1): 276–283. doi:10.1074/jbc.M805061200. {{cite journal}}: |access-date= requires |url= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: unflagged free DOI (link)

Further reading

  • Miallau, L (2009 Jan 2). "Structure and proposed activity of a member of the VapBC family of toxin-antitoxin systems. VapBC-5 from Mycobacterium tuberculosis". The Journal of biological chemistry. 284 (1): 276–83. PMID 18952600. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Arcus, VL (2005 Aug). "The PIN-domain toxin-antitoxin array in mycobacteria". Trends in microbiology. 13 (8): 360–5. PMID 15993073. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

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