InP Quantum Dots: Probing the Active Domain of Tau Peptide Using Energy Transfer

Aggregation of Tau, a natively unfolded protein, is responsible for tauopathies, a class of neurodegenerative disorders. An active peptide sequence containing 20 amino acids is selected from the Tau microtubule binding region, which includes the essential V306-K311 residue, to monitor the structural change that initiates aggregation at very low concentrations. The synthesis of a peptide sequence is accomplished by employing solid-phase protocols. The active domain of Tau possesses an amino functionality on lysine and free thiol on cysteine. The former end is selectively labeled to rhodamine 101 which is further bound to the InP/ZnS quantum dot surface through the thiol linkage. Efficient resonance energy transfer is observed in its unfolded conformation which is confirmed using various steady state fluorescence techniques. The average distance between the quantum dot core and the chromophore is probed by Förster resonance energy transfer (FRET) as 24.5 ± 0.8 Å. Heparin, a negatively charged glycosaminoglycan, is used for inducing aggregation of the active domain of the Tau peptide. Structural changes in the peptide monomer, on addition of heparin, could be monitored at nanomolar concentrations through the inhibition of energy transfer from quantum dots to rhodamine dye.