title: Nonequilibrium synthesis and assembly of hybrid inorganic-protein nanostructures using an engineered DNA binding protein.
abstract: 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 Cu(2)O 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 Cu(2)O binding sequence, designated CN225, that is inserted into a permissive site in TraI. When TraIi1753::CN225 is included in the precursor electrolyte, stable Cu(2)O nanoparticles form, even though the concentrations of [Cu(+)] and [OH(-)] are at 5% of the solubility product (K(sp,Cu2O)). Negative control experiments verify that Cu(2)O 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 Cu(2)O core is surrounded by an adsorbed protein shell. Quantitative protein adsorption studies show that the unexpected stability of Cu(2)O is imparted by the nanomolar surface binding affinity of TraIi1753::CN225 for Cu(2)O (K(d) = 1.2 x 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.
authors.affiliation: Departments of Chemical Engineering, Materials Science and Engineering, and Microbiology, University of Washington, Seattle, WA 98195-1750, USA.
authors.forename: Haixia
authors.initials: H
authors.lastname: Dai
authors.forename: Woo-Seok
authors.initials: WS
authors.lastname: Choe
authors.forename: Corrine K
authors.initials: CK
authors.lastname: Thai
authors.forename: Mehmet
authors.initials: M
authors.lastname: Sarikaya
authors.forename: Beth A
authors.initials: BA
authors.lastname: Traxler
authors.forename: François
authors.initials: F
authors.lastname: Baneyx
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Schwartz
mesh_terms: D000327:Adsorption; D001665:Binding Sites; D003300:Copper / Q000737:chemistry; D004265:DNA Helicases / Q000235:genetics; D004268:DNA-Binding Proteins / Q000138:chemical synthesis / Q000235:genetics / Q000494:pharmacology*; D029968:Escherichia coli Proteins; D049329:Nanostructures / Q000737:chemistry*; D015202:Protein Engineering
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D003300:Copper; C027093:TraI protein, E coli; D004265:DNA Helicases; C030973:cupric oxide