MadSci Network: Biochemistry |
hi Thomas,
Thanks for this very interesting question. I did a little research and came across this paper in the Journal of Histochemistry and Cytochemistry:
Anyang Suna, Xuan V. Nguyena, and Guoying Binga (2002) Comparative Analysis of an Improved Thioflavin-S Stain, Gallyas Silver Stain, and Immunohistochemistry for Neurofibrillary Tangle Demonstration on the Same Sections Journal of Histochemistry and Cytochemistry, Vol. 50, 463-472.
It's a free access article, so anyone can read it. The authors describe an improved method for staining amyloid fibrils using thioflavine-S and feel that their improvement "warrants further inquiry into the mechanisms of these stains". They continue:
"The low background staining indicates that a large array of beta-sheet structure is required for binding because thioflavin-S does not appear to stain native proteins that have only a few relatively isolated beta-strands. Previously proposed models hypothesize that a minimum of five adjacent beta-sheet strands is necessary for Congo red (Klunk et al. 1989 Down), and a similar requirement may apply to thioflavin-S."
So it seems that the dye is quite specific for beta-sheet amyloid structures. When the dye binds, it undergoes a shift in its fluorescent excitation spectrum, which is why it's used for fluorescent staining.
The NCBI has a database named PubChem, where you can search for information on chemical compounds.
It turns out that thioflavin-S is also referred to as Direct Yellow or primuline (and may be spelled thioflavin/thioflavine), so there are some more search engine terms for you. We can see its structure here:
This gives us a good clue as to how it binds amyloid fibrils. It's an elongated structure with both hydrophobic aromatic rings and reactive charged centres. Presumably this allows it to intercalate between adjacent beta-strands and interact strongly with the protein surface.
Hope that helps you,
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