Selective Binding of Thioflavin T in Sequence-Exchanged Single Strand DNA Oligomers and Further Interaction with Phospholipid Membranes

摘要

Selectivity of ThT towards sequence exchanged single strand DNA (ssDNA) oligomers in absence and presence of surface charged lipid vesicles has been studied in detail. The dye shows special affinity for TCTTA sequence with its –N(CH_3)_3structural counterpart and π-interaction with adenine in 5’- CCCTCTTAACCC-3’ (TC4). However, fluorescence spectroscopy and molecular docking suggest that the dye is perfectly aligned with the TAA sequence in 5’-CCCTTAATCCCC-3’ (TT4). Inter- actions with cationic and anionic lipid vesicles were studied to understand the biological relevance in specificity of ThT bind- ing to ssDNA oligomers. Fluorescence intensity of ThT increases significantly due to interaction with charged liposomes along with a considerable hypsochromic shift. Interestingly, evolution of a shoulder at 465 nm was observed solely in cationic lipid membranes due to ThT-dimer formation. It is concluded that the ssDNA bound ThT penetrates the hydrophobic bilayer of the anionic vesicles. However, they attach superficially to the cationic vesicles facilitating dimer formation. Exchange of the nucleotide sequence in ssDNA led to change in the excited state lifetime of bound ThT in anionic liposomes.