Understanding the Self-Assembly of Proteins onto Gold Nanoparticles and Quantum Dots Driven by Metal-Histidine Coordination

Abstract

Coupling of polyhistidine-appended biomolecules to inorganic nanocrystals driven by metal-affinity interactions is a greatly promising strategy to form hybrid bioconjugates. It is simple to implement and can take advantage of the fact that polyhistidine-appended proteins and peptides are routinely prepared using well established molecular engineering techniques. A few groups have shown its effectiveness for coupling proteins onto Zn- or Cd-rich semiconductor quantum dots (QDs). Expanding this conjugation scheme to other metal-rich nanoparticles (NPs) such as AuNPs would be of great interest to researchers actively seeking effective means for interfacing nanostructured materials with biology. In this report, we investigated the metal-affinity driven self-assembly between AuNPs and two engineered proteins, a His7-appended maltose binding protein (MBP-His) and a fluorescent His6-terminated mCherry protein. In particular, we investigated the influence of the capping ligand affinity to the nanoparticle surface, its density, and its lateral extension on the AuNP-protein self-assembly. Affinity gel chromatography was used to test the AuNP-MPB-His7 self-assembly, while NP-to-mCherry-His6 binding was evaluated using fluorescence measurements. We also assessed the kinetics of the self-assembly between AuNPs and proteins in solution, using time-dependent changes in the energy transfer quenching of mCherry fluorescent proteins as they immobilize onto the AuNP surface. This allowed determination of the dissociation rate constant, Kd(-1) ∼ 1-5 nM. Furthermore, a close comparison of the protein self-assembly onto AuNPs or QDs provided additional insights into which parameters control the interactions between imidazoles and metal ions in these systems.

Colloidal nanoparticles as advanced biological sensors

“…Oligohistidines are excellent alternative bioconjugation vectors, as they can bind directly to particle surfaces, sitting between surface ligands. They have been used on both QDs and AuNPs (54). A short sequence of histidine amino acids can be included in a recombinant protein (54), in a peptide sequence (55), or as part of an oligonucleotide construct (56), and its high affinity for metal nanoparticle surfaces allows attachment with excellent control over number and orientation of attached species.…”

“…They have been used on both QDs and AuNPs (54). A short sequence of histidine amino acids can be included in a recombinant protein (54), in a peptide sequence (55), or as part of an oligonucleotide construct (56), and its high affinity for metal nanoparticle surfaces allows attachment with excellent control over number and orientation of attached species. The many emerging highly site-or sequence-selective conjugation techniques, such as click reactions (57,58), strain-promoted cycloadditions (59), and enzyme-mediated ligations (60,61), are excellent prospects for nanoparticle bioconjugation, as they offer rapid, efficient, and strong binding.…”

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating

“…10,127,148 (3) Thiol (-SH) reactive maleimide coupling to cysteine or (sulfhydryl)-modified proteins and peptides, starting with the transformation of the surface reactive groups on the nanocrystals. 216,217 (4) Metal-affinity driven self-assembly between polyhsitidine-appended biomolecules and metal-rich nanocrystals; 161,162,218 this method relies on the affinity between polyhistidine tags and certain transition metal ions (e.g., Ni and Zn), and requires direct interactions between the imidazole groups (on the tag) and the metal-rich surface of nanoparticles. (5) Azide-alkyne Huisgen cycloaddition (or ''Click'' reaction), which requires access to biomolecules premodified with either alkynes or azides, together with azide-or alkyne-functionalized nanoparticles.…”

“…Its use as a conjugation strategy is still somewhat limited, because it requires direct access of the imidazole residues to the inorganic surface of the nanocrystals, although it has been gaining interest in the past few years. 159,162,223,224 The original azide-alkyne Huisgen cycloaddition reaction requires a copper catalyst in particular when using alkyne-modified molecules. 225,226 It has been applied to non-fluorescent NPs such as Fe 3 O 4 nanocrystals.…”

Copolymerization and Synthesis of Multiply Binding Histamine Ligands for the Robust Functionalization of Quantum Dots

“…11 However, due to the limited solution stability of QDs with monodentate ligands in water, 12 several groups have explored the possibility of using polymeric ligands instead. 3,4,13 CdSe/ZnS core−shell quantum dots have been ligand exchanged with polymers including poly(N,N-dimethylaminoacetyl methacrylate), 7 which presents pendant tertiary amine nucleophiles for coordination to the quantum dot surface. Another class of polymeric ligands for quantum dot functionalization include imidazole functionalized polymers, which have shown superior binding capabilities and maintenance of high quantum yields when bound to QDs.…”