The fluorescent characterization of the polymerized microtubule-associated protein Tau.

A new fluorescence formed while microtubule-associated protein tau was incubated at 25 and 37C for hours, with its maximum excitation at 230 and 280 nm, respectively. The fluorescence completely formed after tau was incubated in phosphate buffer and Tris-HCl buffer for approximately 20 h, with a relaxation phase about 2-4 h. The light scattering of the sample solution improved during formation of the fluorescence when tau was incubated. Both the fluorescence and tau oligomers did not form when tau was incubated in the buffers containing DTT. On the other hand, heparin improved both tau aggregation and the fluorescence formation. It suggests that the fluorescence comes from tau polymerization, which may follow the mechanism of tyrosine-tyrosinate emission for a protein not containing any tryptophan residues. This new fluorescence could be used as a probe to tau polymers.