Intein-mediated site-specific conjugation of Quantum Dots to proteins in vivo

We describe an intein based method to site-specifically conjugate Quantum Dots (QDs) to target proteins in vivo. This approach allows the covalent conjugation of any nanostructure and/or nanodevice to any protein and thus the targeting of such material to any intracellular compartment or signalling complex within the cells of the developing embryo. We genetically fused a pleckstrin-homology (PH) domain with the N-terminus half of a split intein (I_N). The C-terminus half (I_C) of the intein was conjugated to QDs in vitro. I_C-QD's and RNA encoding PH-I_N were microinjected into Xenopus embryos. In vivo intein-splicing resulted in fully functional QD-PH conjugates that could be monitored in real time within live embryos. Use of Near Infra Red (NIR)-emitting QDs allowed monitoring of QD-conjugates within the embryo at depths where EGFP is undetectable demonstrating the advantages of QD's for this type of experiment. In conclusion, we have developed a novel in vivo methodology for the site-specific conjugation of QD's and other artificial structures to target proteins in different intracellular compartments and signaling complexes.