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Tagetitoxin

Tagetitoxin
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Proposed structure of tagetitoxin
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Tagetitoxin (TGT) is a bacterial phytotoxin produced by Pseudomonas syringae pv. tagetis.[1][2]

Chemical structure

When TGT was first isolated, it was only partially characterized.[2] The first proposed chemical structure of TGT involved an eight-membered ring,[3] but this was revised shortly afterward to a bicyclic structure (shown at right) based on NMR and mass spectrometry.[4] This structure, however, has been questioned.[5] The absolute configuration remains undetermined, and attempts at confirming the structure by organic synthesis are underway.[6][7][8][9][10][11][12]

Mechanism of action

TGT interferes with development of chloroplasts in young plant leaves thereby causing chlorosis.[13] The natural target of the toxin is chloroplast RNA polymerase. Chloroplast RNA polymerase belongs to ubiquitous family of multisubunit RNA polymerases (RNAP) and is most closely related to bacterial enzymes. In vitro, TGT inhibits bacterial RNAPs from Escherichia coli and Thermus thermophilus, and eukaryotic RNA polymerase III.[14] In contrast, eukaryotic RNA polymerase I and II as well as single-subunit RNA polymerases of bacteriophage T7 and SP6 are relatively insensitive to the compound. TGT binds in the RNAP active site[15] and inhibits initiation and elongation phases of transcription as well as pyrophosphorolysis of the nascent RNA.[15] However, the detailed mechanism of inhibition remains a subject of heated debate.[16][17]

It has been suggested that TGT forms a ternary RNAP-NTP-TGT complex and inhibits phosphodiester bond synthesis either by binding an inhibitory magnesium ion[15] or by trapping a flexible active site domain in an inactive conformation.[18] The third theory suggests that TGT forms predominantly a binary RNAP-TGT complex and inhibits RNAP translocation along the DNA by mimicking the transcription byproduct pyrophosphate.[19]

References

  1. ^ Trimboli, D; Fahy, PC; Baker, KF (1978). "Apical chlorosis and leaf spot of Tagetes spp. Caused by Pseudomonas tagetis Hellmers". Australian Journal of Agricultural Research 29 (4): 831–9. doi:10.1071/AR9780831. 
  2. ^ a b Mitchell, R. E.; Durbin, R. D. (1981). "Tagetitoxin, a toxin produced by Pseudomonas syringae pv. tagetis: purification and partial characterization". Physiological Plant Pathology 18 (2): 157–68. doi:10.1016/S0048-4059(81)80037-9. 
  3. ^ Mitchell, R. E.; Durbin, R. D. (1983). "The structure of tagetitoxin, a phytotoxin of Pseudomonas syringae pv. Tagetis". Phytochemistry 22 (6): 1425. doi:10.1016/S0031-9422(00)84028-5. 
  4. ^ Mitchell, R. E.; Coddington, J. M.; Young, H. (1989). "A revised structure for tagetitoxin". Tetrahedron Lett. 30 (4): 501. doi:10.1016/S0040-4039(00)95239-0. 
  5. ^ Gronwald, J.W.; Plaisance, K. L.; Marimanikkuppam, S.; Ostrowski, B. G. (2005). "Tagetitoxin purification and partial characterization". Physiol. Mol. Plant Pathol. 67: 23. doi:10.1016/j.pmpp.2005.09.002. 
  6. ^ Porter, Michael; Plet, Julien; Sandhu, Amandeep; Sehailia, Moussa (2009). "Thieme Chemistry Journal Awardees - Where Are They Now? Approaches to Tagetitoxin and its Decarboxy Analogue from d-Glucose". Synlett 2009 (20): 3258. doi:10.1055/s-0029-1218525. 
  7. ^ Mortimer, Anne J. Price; Aliev, Abil E.; Tocher, Derek A.; Porter, Michael J. (2008). "Synthesis of the Tagetitoxin Core via Photo-Stevens Rearrangement". Organic Letters 10 (23): 5477–80. PMID 18973329. doi:10.1021/ol802297h. 
  8. ^ Sammakia, T.; Hurley, T. B.; Sammond, D. M.; Smith, R. S.; Sobolov, S. B.; Oeschger, T. R. (1996). "Dihydroxylation and oxidative cleavage of olefins in the presence of sulfur". Tetrahedron Lett. 37 (26): 4427. doi:10.1016/0040-4039(96)00879-9. 
  9. ^ Dent, B. R.; Furneaux, R. H.; Gainsford, G. J.; Lynch, G. P. (1999). "Synthesis studies of structural analogues of tagetitoxin: 2-phosphate". Tetrahedron 55 (22): 6977. doi:10.1016/S0040-4020(99)00327-0. 
  10. ^ Plet, Julien R. H.; Porter, Michael J. (2006). "Synthesis of the bicyclic core of tagetitoxin". Chemical Communications (11): 1197–9. PMID 16518489. doi:10.1039/B600819D. 
  11. ^ Mortimer, Anne J. P.; Plet, Julien R. H.; Obasanjo, Oluwafunsho A.; Kaltsoyannis, Nikolas; Porter, Michael J. (2012). "Inter- and intramolecular reactions of 1-deoxy-1-thio-1,6-anhydrosugars with α-diazoesters: synthesis of the tagetitoxin core by photochemical ylide rearrangement". Org. Biomol. Chem. 10 (43): in press. doi:10.1039/c2ob26308d. ,
  12. ^ Sehailia, Moussa (2011). Studies towards the total synthesis of tagetitoxin (Doctoral thesis). University College London. [page needed]
  13. ^ Lukens, J. H.; Durbin, R. D. (1985). "Tagetitoxin affects plastid development in seedling leaves of wheat". Planta 165 (3): 311–21. PMID 24241135. doi:10.1007/BF00392227. 
  14. ^ Steinberg, Thomas H.; Mathews, Dennis E.; Durbin, Richard D.; Burgess, Richard R. (1990). "Tagetitoxin: A New Inhibitor of Eukaryotic Transcription by RNA Polymerase III". The Journal of Biological Chemistry 265 (1): 499–505. PMID 2403565. 
  15. ^ a b c Vassylyev, Dmitry G; Svetlov, Vladimir; Vassylyeva, Marina N; Perederina, Anna; Igarashi, Noriyuki; Matsugaki, Naohiro; Wakatsuki, Soichi; Artsimovitch, Irina (2005). "Structural basis for transcription inhibition by tagetitoxin". Nature Structural & Molecular Biology 12 (12): 1086–93. PMC 1790907. PMID 16273103. doi:10.1038/nsmb1015. 
  16. ^ Klyuyev, Sergiy; Vassylyev, Dmitry G. (2012). "The binding site and mechanism of the RNA polymerase inhibitor tagetitoxin: An issue open to debate". Transcription 3 (2): 46–50. PMC 3337825. PMID 22414754. doi:10.4161/trns.19468. 
  17. ^ Svetlov, Vladimir; Artsimovitch, Irina; Nudler, Evgeny (2012). "Response to Klyuyev and Vassylyev: On the mechanism of tagetitoxin inhibition of transcription". Transcription 3 (2): 51–5. PMC 3337826. PMID 22414748. doi:10.4161/trns.19749. 
  18. ^ Artsimovitch, Irina; Svetlov, Vladimir; Nemetski, Sondra Maureen; Epshtein, Vitaly; Cardozo, Timothy; Nudler, Evgeny (2011). "Tagetitoxin Inhibits RNA Polymerase through Trapping of the Trigger Loop". The Journal of Biological Chemistry 286 (46): 40395–400. PMC 3220573. PMID 21976682. doi:10.1074/jbc.M111.300889. 
  19. ^ Malinen, Anssi M.; Turtola, Matti; Parthiban, Marimuthu; Vainonen, Lioudmila; Johnson, Mark S.; Belogurov, Georgiy A. (2012). "Active site opening and closure control translocation of multisubunit RNA polymerase". Nucleic Acids Research 40 (15): 7442–51. PMC 3424550. PMID 22570421. doi:10.1093/nar/gks383.