We report a virus-based scaffold for the synthesis of single-crystal ZnS, CdS, and freestanding chemically ordered CoPt and FePt nanowires, with the means of modifying substrate specificity through standard biological methods. Peptides (selected through an evolutionary screening process) that exhibit control of composition, size, and phase during nanoparticle nucleation have been expressed on the highly ordered filamentous capsid of the M13 bacteriophage. The incorporation of specific, nucleating peptides into the generic scaffold of the M13 coat structure provides a viable template for the directed synthesis of semiconducting and magnetic materials. Removal of the viral template by means of annealing promoted oriented aggregation-based crystal growth, forming individual crystalline nanowires. The unique ability to interchange substrate-specific peptides into the linear self-assembled filamentous construct of the M13 virus introduces a material tunability that has not been seen in previous synthetic routes. Therefore, this system provides a genetic toolkit for growing and organizing nanowires from semiconducting and magnetic materials.

The highly organized structure of M13 bacteriophage was used as an evolved biological template for the nucleation and orientation of semiconductor nanowires. To create this organized template, peptides were selected by using a pIII phage display library for their ability to nucleate ZnS or CdS nanocrystals. The successful peptides were expressed as pVIII fusion proteins into the crystalline capsid of the virus. The engineered viruses were exposed to semiconductor precursor solutions, and the resultant nanocrystals that were templated along the viruses to form nanowires were extensively characterized by using high-resolution analytical electron microscopy and photoluminescence. ZnS nanocrystals were well crystallized on the viral capsid in a hexagonal wurtzite or a cubic zinc blende structure, depending on the peptide expressed on the viral capsid. Electron diffraction patterns showed single-crystal type behavior from a polynanocrystalline area of the nanowire formed, suggesting that the nanocrystals on the virus were preferentially oriented with their [001] perpendicular to the viral surface. Peptides that specifically directed CdS nanocrystal growth were also engineered into the viral capsid to create wurtzite CdS virus-based nanowires. Lastly, heterostructured nucleation was achieved with a dual-peptide virus engineered to express two distinct peptides within the same viral capsid. This work represents a genetically controlled biological synthesis route to a semiconductor nanoscale heterostructure.

1. The M2 protein of influenza A virus is implicated in transmembrane pH regulation during infection. Whole‐cell patch clamp of mouse erythroleukaemia cells expressing the M2 protein in the surface membrane showed a conductance due to M2 which was specifically blocked by the anti‐influenza drug rimantadine. 2. The ion selectivity of the rimantadine‐sensitive current through M2 was determined. Reversal potentials were close to equilibrium potentials for transmembrane pH gradients and not to those for Na+, K+ or Cl‐ concentration gradients. M2 permeability to Na+ relative to H+ was estimated to be less than 6 x 10(‐7). 3. The M2 conductance increased as external pH decreased below 8.5 and approached saturation at an external pH of 4, effects attributable to increased permeability due to increased driving potential and to activation by low external pH. Both activation and permeation could be described by interaction of protons with sites on M2, with apparent dissociation constants of approximately 0.1 microM and 1 microM, respectively, under physiological conditions. 4. The M2 protein can transfer protons selectively across membranes with the H+ electrochemical gradient, properties consistent with its role in modifying virion and trans‐Golgi pH during virus infection.

Anchored periplasmic expression (APEx) is a technology for the isolation of ligand-binding proteins from combinatorial libraries anchored on the periplasmic face of the inner membrane of Escherichia coli . After disruption of the outer membrane by Tris-EDTA-lysozyme, the inner-membrane-anchored proteins readily bind fluorescently labeled ligands as large as 240 kDa. Fluorescently labeled cells are isolated by flow cytometry, and the DNA of isolated clones is rescued by PCR. By using two rounds of APEx, the affinity of a neutralizing antibody to the Bacillus anthracis protective antigen was improved >200-fold, exhibiting a final K _D of 21 pM. This approach has several technical advantages compared with previous library screening technologies, including the unique ability to screen for ligand-binding proteins that bind endogenously expressed ligands fused to a short-lived GFP. Further, APEx is able to display proteins either as an N - terminal fusion to a six-residue sequence derived from the native E. coli lipoprotein NlpA, or as a C-terminal fusion to the phage gene three minor coat protein of M13. The latter fusions allow hybrid phage display/APEx strategies without the need for further subcloning.