Synthesizing and Modifying Peptides for Chemoselective Ligation and Assembly into Quantum Dot-Peptide Bioconjugates
Quantum dots (QDs) are well-established as photoluminescent nanoparticle probes for in vitro or in vivo imaging, sensing, and even drug delivery. A critical component of this research is the need to reliably conjugate peptides, proteins, oligonucleotides, and other biomolecules to QDs in a controlled manner. In this chapter, we describe the conjugation of peptides to CdSe/ZnS QDs using a combination of polyhistidine self-assembly and hydrazone ligation. The former is a high-affinity interaction with the inorganic surface of the QD; the latter is a highly efficient and chemoselective reaction that occurs between 4-formylbenzoyl (4FB) and 2-hydrazinonicotinoyl (HYNIC) moieties. Two methods are presented for modifying peptides with these functional groups: (1) solid phase peptide synthesis; and (2) solution phase modification of pre-synthesized, commercial peptides. We further describe the aniline-catalyzed ligation of 4FB- and HYNIC-modified peptides, in the presence of a fluorescent label on the latter peptide, as well as subsequent assembly of the ligated peptide to water-soluble QDs. Many technical elements of these protocols can be extended to labeling peptides with other small molecule reagents. Overall, the bioconjugate chemistry is robust, selective, and modular, thereby potentiating the controlled conjugation of QDs with a diverse array of biomolecules for various applications.
Key wordsQuantum dot Peptide Bioconjugation Polyhistidine Self-assembly Chemoselective ligation Hydrazone
The authors acknowledge NRL, NRL NSI, ONR, and DTRA-JSTO MIPR # B112582M for financial support. W.R.A. is grateful to the Natural Sciences and Engineering Research Council of Canada (NSERC) for support through a postdoctoral fellowship. J.B.B.-C. acknowledges a Marie Curie IOF. RLM thanks National Science Foundation Graduate Research Fellowship (Grant no. DGE-0750616) for support.
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