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Thioflavin T
Thioflavin T.svg
IUPAC name
4-(3,6-dimethyl-1,3-benzothiazol-3-ium-2-yl)-N,N-dimethylaniline chloride
3D model (JSmol)
ECHA InfoCard 100.017.482
Molar mass 318.86 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Thioflavin is also known as Basic yellow 1 or Methylene yellow and has resonance peaks at 410-420nm and 211nm. It is a fluorescent dye. It is corrosive, an acute toxic and an irritant. As of 18 August 2019, 584 articles mentioned alzheimer disease alongside it, and 231 articles mentioned neurodegenerative diseases alongside it, and 139 articles mention insulin alongside it. It was also listed as a drug for dermatological disorders and genital disorders. It is toxic if swallowed and causes serious eye damage.[1] It is a benzothiazole dye.[2]

Thioflavin is available as at least two compounds, listed below as Thioflavin T and Thioflavin S. Both are used as dyes for histology staining and biophysical studies of protein aggregation,[3] specifically it has been used since 1989 to investigate amyloid formation.[2] They are also used in biophysical studies of the electrophysiology of bacteria.[4]

Thioflavin T

Thioflavin T (Basic Yellow 1, CI 49005, or ThT) is a benzothiazole salt obtained by the methylation of dehydrothiotoluidine with methanol in the presence of hydrochloric acid. The dye is widely used to visualize and quantify the presence of misfolded protein aggregates called amyloid, both in vitro and in vivo (e.g., plaques composed of amyloid beta found in the brains of Alzheimer's disease patients).[3]

When it binds to beta sheet-rich structures, such as those in amyloid aggregates, the dye displays enhanced fluorescence and a characteristic red shift of its emission spectrum.[5][6] Additional studies also consider fluorescence changes as result of the interaction with double stranded DNA.[7] This change in fluorescent behavior can be caused by many factors that affect the excited state charge distribution of thioflavin T, including binding to a rigid, highly-ordered nanopocket, and specific chemical interactions between ThT and the nanopocket.[8][9]

Prior to binding to an amyloid fibril, ThT emits weakly around 527 nm. Quenching effects of the nearby excitation peak at 450 nm is suspected to play a role in minimizing emissions.

When excited at 450 nm, ThT produces a strong fluorescence signal at approximately 482 nm upon binding to amyloids. ThT molecule consists of a benzylamine and a benzathiole ring connected through a carbon-carbon bond. These two rings can rotate freely when the molecule is in solution. The free rotation of these rings results in quenching of any excited state generated by photon excitation. However, when ThT binds to amyloid fibrils, the two rotational planes of the two rings become immobilized and therefore, this molecule can maintain its excited state.[3]

Thioflavin T fluorescence is often used as a diagnostic of amyloid structure, but it is not perfectly specific for amyloid. Depending on the particular protein and experimental conditions, thioflavin T may[8] or may not[10] undergo a spectroscopic change upon binding to precursor monomers, small oligomers, unaggregated material with a high beta sheet content, or even alpha helix-rich proteins. Conversely, some amyloid fibers do not affect thioflavin T fluorescence,[11] raising the prospect of false negative results.

X-ray crystal structure of thioflavin T bound to an amyloid-like oligomer of ?2 microglobulin
Structure of thioflavin T bound to an amyloid-like oligomer of ?2 microglobulin (in gray), in a complex that displays enhanced and red shifted fluorescence. Many factors that shift the excited state charge from the dimethylaminobenzyl portion of thioflavin T (in blue) to the benzothiazole portion (in red), including binding to rigid, highly-ordered amyloid aggregates, can produce this 'positive' thioflavin T signal.[8]
Thioflavin S stain (left in green) and amyloid-Beta antibody immunocytochemistry (right) on adjacent sections of the hippocampus of a patient suffering from Alzheimer's disease. Thioflavin S binds both senile plaques (SP) and neurofibrillary tangles (NFT), the two characteristic cortical lesions of Alzheimer's. Amyloid beta is a peptide derived from the amyloid precursor protein which is only found in senile plaques, and so only plaques are visible in the right hand image. The left image also has a red signal which exactly superimposes the green signal in lipofuscin granules (LP), which are autofluorescent inclusions derived from lysosomes which accumulate in the human brain during normal aging.

In adult C. elegans, exposure to thioflavin T results "in a profoundly extended lifespan and slowed aging" at some levels, but decreased lifespan at higher levels.[12]

Thioflavin S

Thioflavin S is a homogenous mixture of compounds that results from the methylation of dehydrothiotoluidine with sulfonic acid. It is also used to stain amyloid plaques. Like thioflavin T it binds to amyloid fibrils but not monomers and gives a distinct increase in fluorescence emission. However unlike thioflavin T, it does not produce a characteristic shift in the excitation or emission spectra.[5] This latter characteristic of thioflavin S results in high background fluorescence, making it unable to be used in quantitative measurements of fibril solutions.[5] Another dye that is used to identify amyloid structure is Congo Red.

See also


  1. ^ "Thioflavin T". National Center for Biotechnology Information. PubChem.
  2. ^ a b Gade Malmos, Kirsten; Blancas-Mejia, Luis M.; Weber, Benedikt; Buchner, Johannes; Ramirez-Alvarado, Marina; Naiki, Hironobu; Otzen, Daniel (2017). "THT 101: A primer on the use of thioflavin T to investigate amyloid formation". Amyloid. 24: 1-16. doi:10.1080/13506129.2017.1304905. PMID 28393556.
  3. ^ a b c Biancalana M, Koide S (July 2010). "Molecular mechanism of Thioflavin-T binding to amyloid fibrils". Biochimica et Biophysica Acta. 1804 (7): 1405-12. doi:10.1016/j.bbapap.2010.04.001. PMC 2880406. PMID 20399286.
  4. ^ Prindle A, Liu J, Asally M, Ly S, Garcia-Ojalvo J, Süel GM (November 2015). "Ion channels enable electrical communication in bacterial communities". Nature. 527 (7576): 59-63. Bibcode:2015Natur.527...59P. doi:10.1038/nature15709. PMC 4890463. PMID 26503040.
  5. ^ a b c H. LeVine III, Methods in Enzymology. 309, 274 (1999)
  6. ^ Groenning M (March 2010). "Binding mode of Thioflavin T and other molecular probes in the context of amyloid fibrils-current status". Journal of Chemical Biology. 3 (1): 1-18. doi:10.1007/s12154-009-0027-5. PMC 2816742. PMID 19693614.
  7. ^ Ilanchelian M, Ramaraj R (2004). "Emission of thioflavin T and its control in the presence of DNA". Journal of Photochemistry and Photobiology A: Chemistry. 162 (1): 129-137. doi:10.1016/s1010-6030(03)00320-4.
  8. ^ a b c Wolfe LS, Calabrese MF, Nath A, Blaho DV, Miranker AD, Xiong Y (September 2010). "Protein-induced photophysical changes to the amyloid indicator dye thioflavin T". Proceedings of the National Academy of Sciences of the United States of America. 107 (39): 16863-8. Bibcode:2010PNAS..10716863W. doi:10.1073/pnas.1002867107. PMC 2947910. PMID 20826442.
  9. ^ Biancardi A, Biver T, Mennucci B (2017). "Fluorescent dyes in the context of DNA-binding: The case of Thioflavin T". Int. J. Quantum Chem. 117 (8): e25349. doi:10.1002/qua.25349.
  10. ^ LeVine H (March 1993). "Thioflavine T interaction with synthetic Alzheimer's disease beta-amyloid peptides: detection of amyloid aggregation in solution". Protein Science. 2 (3): 404-10. doi:10.1002/pro.5560020312. PMC 2142377. PMID 8453378.
  11. ^ Cloe AL, Orgel JP, Sachleben JR, Tycko R, Meredith SC (March 2011). "The Japanese mutant A? (?E22-A?(1-39)) forms fibrils instantaneously, with low-thioflavin T fluorescence: seeding of wild-type A?(1-40) into atypical fibrils by ?E22-A?(1-39)". Biochemistry. 50 (12): 2026-39. doi:10.1021/bi1016217. PMC 3631511. PMID 21291268.
  12. ^ Alavez S, Vantipalli MC, Zucker DJ, Klang IM, Lithgow GJ (April 2011). "Amyloid-binding compounds maintain protein homeostasis during ageing and extend lifespan". Nature. 472 (7342): 226-9. Bibcode:2011Natur.472..226A. doi:10.1038/nature09873. PMC 3610427. PMID 21451522.

External links

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