Thioflavin T forms a non-fluorescent complex with a-helical poly-L-glutamic acid

摘要

Since its debut in the field of in vitro biophysics, Thioflavin T has become the most widely used amyloid-specific fluorescent stain.1 Although there are competing models of the binding interactions and mechanisms of the powerful fluorescence enhancement in ThT-amyloid complexes,1-3 the prevailing notion is that ThT binds specifically to multistranded P-sheets, such as those constituting amyloid fibrils. As a molecular rotor, ThT requires tight entrapment and planarization of the conformation (within amyloid fibril's moieties) for the luminescence to occur.4'5 Exceptionally, as is the case of the complex between ThT and an a-helical protein, acetylocholinesterase,6 the planarised and therefore fluorescing conformation of the dye may be enforced by n-n stacking interactions with aromatic residues in the absence of a β-sheet structure. The importance of π-π interactions has been also emphasized in studies on binding of ThT to β-sheet-forming peptides.7'8 On the other hand, our recent work on the so-called β2-type fibrils formed by PLGA suggests that interactions between ThT and aromatic side chains are not necessary to enhance fluorescence of amyloid-bound ThT molecules.9