Nonequilibrium Synthesis and Assembly of Hybrid Inorganic−Protein Nanostructures Using an Engineered DNA Binding Protein

• Published in: Journal of the American Chemical Society 2005-11, Vol.127 (44), p.15637-15643
• Main Authors: Dai, Haixia, Choe, Woo-Seok, Thai, Corrine K, Sarikaya, Mehmet, Traxler, Beth A, Baneyx, François, Schwartz, Daniel T
• Format: Article
• Language: English
• Subjects: Adsorption; Binding Sites; Biological and medical sciences; Copper - chemistry; DNA Helicases - genetics; DNA-Binding Proteins - chemical synthesis; DNA-Binding Proteins - genetics; DNA-Binding Proteins - pharmacology; Escherichia coli Proteins; Fundamental and applied biological sciences. Psychology; Interactions. Associations; Intermolecular phenomena; Molecular biophysics; Nanostructures - chemistry; Protein Engineering
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja055499h

We show that a protein with no intrinsic inorganic synthesis activity can be endowed with the ability to control the formation of inorganic nanostructures under thermodynamically unfavorable (nonequilibrium) conditions, reproducing a key feature of biological hard-tissue growth and assembly. The nonequilibrium synthesis of Cu2O nanoparticles is accomplished using an engineered derivative of the DNA-binding protein TraI in a room-temperature precursor electrolyte. The functional TraI derivative (TraIi1753::CN225) is engineered to possess a cysteine-constrained 12-residue Cu2O binding sequence, designated CN225, that is inserted into a permissive site in TraI. When TraIi1753::CN225 is included in the precursor electrolyte, stable Cu2O nanoparticles form, even though the concentrations of [Cu+] and [OH-] are at 5% of the solubility product (K sp,Cu 2 O). Negative control experiments verify that Cu2O formation is controlled by inclusion of the CN225 binding sequence. Transmission electron microscopy and electron diffraction reveal a core−shell structure for the nonequilibrium nanoparticles:  a 2 nm Cu2O core is surrounded by an adsorbed protein shell. Quantitative protein adsorption studies show that the unexpected stability of Cu2O is imparted by the nanomolar surface binding affinity of TraIi1753::CN225 for Cu2O (K d = 1.2 × 10-8 M), which provides favorable interfacial energetics (−45 kJ/mol) for the core−shell configuration. The protein shell retains the DNA-binding traits of TraI, as evidenced by the spontaneous organization of nanoparticles onto circular double-stranded DNA.