Multiple and Cooperative Binding of Fluorescence Light-up Probe Thioflavin T with Human Telomere DNA G-Quadruplex.

Thioflavin T (ThT), a typical probe for protein fibrils, also binds human telomeric G-quadruplex with a fluorescent light-up signal change and high specificity against DNA duplexes. Cell penetration and low cytotoxicity of fibril probes having been widdely established, modifying ThT and other fibril probes is an attractive means of generating new G-quadiuplex ligands. Thus, elucidating the binding mechanism is important for the design of new drugs and fluorescent probes based on ThT. Here, we investigated the binding mechanism of ThT with several variants of the human telomeric sequence in the presence of monovalent cations. Fluorescence titrations and electrospray ionization mass spectrometry (ESl-MS) analyses demonstrated that each G-quadruplex unit cooperatively binds to several ThT molecules. ThT brightly fluoresces when a single ligand is bound to the G-quadruplex and is quenched as ligand binding stoichiometry increases. Both the light-up signal and the dissociation constants are exquisitely sensitive to the base sequence and to the G-quadrupIex structure. These results are crudal for the sensible design and interpretation of G-quadruplex detection assays using fluorescent ligands in general and ThT in particular. [ABSTRACT FROM AUTHOR]