Carbon nanotubes have properties potentially useful in diverse electrical and mechanical nanoscale devices and for making strong, light materials. However, carbon nanotubes are difficult to solubilize and organize into architectures necessary for many applications. In the present paper, we describe an amphiphilic alpha-helical peptide specifically designed not only to coat and solubilize carbon nanotubes, but also to control the assembly of the peptide-coated nanotubes into macromolecular structures through peptide-peptide interactions between adjacent peptide-wrapped nanotubes. The data presented herein show that the peptide folds into an amphiphilic alpha-helix in the presence of carbon nanotubes and disperses them in aqueous solution by noncovalent interactions with the nanotube surface. Electron microscopy and polarized Raman studies reveal that the peptide-coated nanotubes assemble into fibers with the nanotubes aligned along the fiber axis. Most importantly, the size and morphology of the fibers can be controlled by manipulating solution conditions that affect peptide-peptide interactions.

The M 2 protein from inf luenza A virus forms proton-selective channels that are essential to viral function and are the target of the drug amantadine. Cys scanning was used to generate a series of mutants with successive substitutions in the transmembrane segment of the protein, and the mutants were expressed in Xenopus laevis oocytes. The effect of the mutations on reversal potential, ion currents, and amantadine resistance were measured. Fourier analysis revealed a periodicity consistent with a four-stranded coiled coil or helical bundle. A three-dimensional model of this structure suggests a possible mechanism for the proton selectivity of the M 2 channel of inf luenza virus.Ion channels are responsible for the rapid and efficient conduction of ions across phospholipid bilayers. They are generally highly selective for their permeant ions, and are gated by voltage or ligands (1). Although a number of high-resolution structures are available for hemolysins (2) and porins (3)-channel-like proteins that form large, nonselective poresstructural analysis of more selective ion channel proteins is at an early stage. Sequence analysis and low-resolution diffraction data indicate that their conduction pathways often consist of bundles of ␣-helices (4, 5), but the determination of high-resolution structures of channel proteins has been hampered by their limited availability and large size.M 2 from influenza virus is an essential component of the viral envelope and forms a highly selective, pH-regulated proton channel that is the target of the anti-influenza drug amantadine (6-9). The influenza virus enters cells through internalization into the endocytic pathway, with virus uncoating taking place in endosomal compartments. The M 2 ion channel activity permits protons to enter the virion interior, and this acidification weakens the interactions of the matrix protein (M 1 ) with the ribonucleoprotein core (10). By comparison to the channels of excitable tissues, M 2 is quite small (97 residues) and contains but one hydrophobic stretch of 18 residues believed to form a transmembrane (TM) helix (residues 26-43). A wealth of experimental evidence indicates that the M 2 channel DPL 26 VVAASIIGILHLILWIL 43 D consists of a tetrameric array of parallel, TM peptides with their N termini directed toward the outside of the virus (6-9). A synthetic 25-residue peptide spanning the hydrophobic region forms amantadine-sensitive proton channels, indicating that the determinants for assembly of the channel lie within this TM peptide (11). Further, CD spectroscopy indicates that this peptide forms ␣-helices in membranes (12). Thus, the TM region of the channel appears to consist of a parallel bundle of ␣-helices.Here we describe the use of Cys-scanning mutagenesis (13,17,18) to obtain more detailed information concerning the arrangement of the TM helices within the tetrameric pore. A similar method has been used previously to infer the probable structures of other homo-oligomeric TM proteins, including glycophorin (14) and phosph...

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Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images.