Formation of an Efficient Energy Transfer Complex between Quantum Dots and Exiguobacterium sibiricum Retinal Protein via the Histidine-Cysteine Anchor

Abstract

Resonance energy transfer in self-assembled hybrid structures formed by water-soluble semiconductor CdSe/ZnS quantum dots (QD) with a cysteine shell and the Exiguobacterium sibiricum retinal protein (ESR) in three modifications, with and without a 6-membered C-terminal histidine tag, and with both the histidine tag and C-terminal cysteine residue. Steady-state and time-resolved fluorescence spectroscopy was used to demonstrate that nonradiative energy transfer from QD onto the ESR protein depends on the strength of intermolecular interactions in the hybrid complex. A shift from electrostatic interactions in the QD-ESR donor-acceptor pair to coordinate bond with an additional disulfide bond resulted in an increase of the energy transfer efficiency from 40 to over 90%. The proposed method to produce noncovalent conjugates from QDs and light-sensitive proteins can be a promising one for biomedical applications, as well as for the development of new solar energy accumulation systems.