S.S. Xie

Very long carbon nanotubes

Carbon nanotubes can now be produced in large quantities by either arc methods, or thermal decomposition of hydrocarbons,. Here we report that pyrolysis of acetylene over iron/silica substrates is an effective method with which to produce very long, multiwalled carbon nanotubes that reach about 2 mm in length, which is an order of magnitude longer than that described in most previous reports,.

Unusual architecture of the p7 channel from hepatitis C virus

The hepatitis C virus (HCV) has developed a small membrane protein, p7, which remarkably can self-assemble into a large channel complex that selectively conducts cations. We wanted to examine the structural solution that the viroporin adopts in order to achieve selective cation conduction, because p7 has no homology with any of the known prokaryotic or eukaryotic channel proteins. The activity of p7 can be inhibited by amantadine and rimantadine, which are potent blockers of the influenza M2 channel and licensed drugs against influenza infections. The adamantane derivatives have been used in HCV clinical trials, but large variation in drug efficacy among the various HCV genotypes has been difficult to explain without detailed molecular structures. Here we determine the structures of this HCV viroporin as well as its drug-binding site using the latest nuclear magnetic resonance (NMR) technologies. The structure exhibits an unusual mode of hexameric assembly, where the individual p7 monomers, i, not only interact with their immediate neighbours, but also reach farther to associate with the i+2 and i+3 monomers, forming a sophisticated, funnel-like architecture. The structure also points to a mechanism of cation selection: an asparagine/histidine ring that constricts the narrow end of the funnel serves as a broad cation selectivity filter, whereas an arginine/lysine ring that defines the wide end of the funnel may selectively allow cation diffusion into the channel. Our functional investigation using whole-cell channel recording shows that these residues are critical for channel activity. NMR measurements of the channel–drug complex revealed six equivalent hydrophobic pockets between the peripheral and pore-forming helices to which amantadine or rimantadine binds, and compound binding specifically to this position may allosterically inhibit cation conduction by preventing the channel from opening. Our data provide a molecular explanation for p7-mediated cation conductance and its inhibition by adamantane derivatives.

Viral proteins function as ion channels

Abstract Viral ion channels are short membrane proteins with 50–120 amino acids and play an important role either in regulating virus replication, such as virus entry, assembly and release or modulating the electrochemical balance in the subcellular compartments of host cells. This review summarizes the recent advances in viral encoded ion channel proteins (or viroporins), including PBCV-1 KcV, influenza M2, HIV-1 Vpu, HCV p7, picornavirus 2B, and coronavirus E and 3a. We focus on their function and mechanisms, and also discuss viral ion channel protein serving as a potential drug target.

Materials - Creating the narrowest carbon nanotubes

The properties of carbon nanotubes depend on their diameter and on the two integers (m,n) that describe their roll-up vector. The smallest nanotube reported previously had a diameter of 0.7 nm, the same as that of a C60 structure, although nanotubes with a diameter of 0.4 nm have been predicted. Here we report that simple improvements in the electric-arc technique can create a carbon nanotube with a diameter of 0.5 nm — the same as a C36 molecule.

PEDV ORF3 encodes an ion channel protein and regulates virus production

Several studies suggest that the open reading frame 3 (ORF3) gene of porcine epidemic diarrhea virus (PEDV) is related to viral infectivity and pathogenicity, but its function remains unknown. Here, we propose a structure model of the ORF3 protein consisting of four TM domains and forming a tetrameric assembly. ORF3 protein can be detected in PEDV‐infected cells and it functions as an ion channel in both Xenopus laevis oocytes and yeast. Mutation analysis showed that Tyr170 in TM4 is important for potassium channel activity. Furthermore, viral production is reduced in infected Vero cells when ORF3 gene is silenced by siRNA. Interestingly, the ORF3 gene from an attenuated PEDV encodes a truncated protein with 49 nucleotide deletions, which lacks the ion channel activity.

Characterization of zinc oxide crystal nanowires grown by thermal evaporation of ZnS powders

Abstract Semiconductor single-crystal ZnO nanowires have been successfully synthesized in bulk quantities by a simple and low cost process based on thermal evaporation of ZnS powders onto silicon substrates with the presence of Au catalyst. XRD of the product proves that the nanowires are the wurtzite structure of ZnO. Scanning electron microscopy and transmission electron microscopy show that the ZnO nanowires have diameters about 20–60 nm and lengths up to several tens of micrometers. The growth of ZnO nanowires is controlled by the conventional vapor–liquid–solid mechanism. The dependence of photoluminescence on temperatures was examined by He–Cd laser.

A simple large-scale synthesis of coaxial nanocables: silicon carbide sheathed with silicon oxide

Abstract We reported a simple method to synthesize coaxial nanocables with silicon carbide core and amorphous silicon oxide sheath just by exposure of Au-coated silicon substrates to carbon monoxide at 1100 °C. The as-grown product was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and micro-Raman spectroscopy. The obtained nanocables were in large scale, several tens of micrometers long, with the core a few nanometers to ten or more nanometers in diameter. The vapor–liquid–solid mechanism was proposed to elucidate the growth process.

DIDS blocks a chloride-dependent current that is mediated by the 2B protein of enterovirus 71

DIDS blocks a chloride-dependent current that is mediated by the 2B protein of enterovirus 71

The ORF4a protein of human coronavirus 229E functions as a viroporin that regulates viral production

Abstract In addition to a set of canonical genes, coronaviruses encode additional accessory proteins. A locus located between the spike and envelope genes is conserved in all coronaviruses and contains a complete or truncated open reading frame (ORF). Previously, we demonstrated that this locus, which contains the gene for accessory protein 3a from severe acute respiratory syndrome coronavirus (SARS-CoV), encodes a protein that forms ion channels and regulates virus release. In the current study, we explored whether the ORF4a protein of HCoV-229E has similar functions. Our findings revealed that the ORF4a proteins were expressed in infected cells and localized at the endoplasmic reticulum/Golgi intermediate compartment (ERGIC). The ORF4a proteins formed homo-oligomers through disulfide bridges and possessed ion channel activity in both Xenopus oocytes and yeast. Based on the measurement of conductance to different monovalent cations, the ORF4a was suggested to form a non-selective channel for monovalent cations, although Li+ partially reduced the inward current. Furthermore, viral production decreased when the ORF4a protein expression was suppressed by siRNA in infected cells. Collectively, this evidence indicates that the HCoV-229E ORF4a protein is functionally analogous to the SARS-CoV 3a protein, which also acts as a viroporin that regulates virus production. This article is part of a Special Issue entitled: Viral Membrane Proteins — Channels for Cellular Networking.

Tunneling into multiwalled carbon nanotubes: Coulomb blockade and the Fano resonance

Tunneling spectroscopy measurements of single tunnel junctions formed between multiwalled carbon nanotubes (MWNTs) and a normal metal are reported. Intrinsic Coulomb interactions in the MWNTs give rise to a strong zero-bias suppression of a tunneling density of states that can be fitted numerically to the environmental quantum-fluctuation theory. An asymmetric conductance anomaly near zero bias is found at low temperatures and interpreted as Fano resonance in the strong tunneling regime.