Peptide nanotube-modified electrodes for enzyme-biosensor applications

The fabrication and notably improved performance of composite electrodes based on modified self-assembled diphenylalanine peptide nanotubes is described. Peptide nanotubes were attached to gold electrodes, and we studied the resulting electrochemical behavior using cyclic voltammetry and chronoamperometry. The peptide nanotube-based electrodes demonstrated a direct and unmediated response to hydrogen peroxide and NADH at a potential of +0.4 V (vs SCE). This biosensor enables a sensitive determination of glucose by monitoring the hydrogen peroxide produced by an enzymatic reaction between the glucose oxidase attached to the peptide nanotubes and glucose. In addition, the marked electrocatalytic activity toward NADH enabled a sensitive detection of ethanol using ethanol dehydrogenase and NAD+. The peptide nanotube-based amperometric biosensor provides a potential new tool for sensitive biosensors and biomolecular diagnostics.     

The effect of chronic L-dopa administration on supersensitive pre- and postsynaptic dopaminergic receptors in rat brain

Chronic administration of haloperidol induced supersensitivity of the pre- and postsynaptic dopaminergic receptors in rat brain. The response of the presynaptic receptors was determined by an enhanced inhibitory effect of apomorphine on dopamine synthesis after gamma-butyrolactone injection. This change in the receptor function was detected both in the nigrostriatal and mesolimbic pathways. Haloperidol also increased the 3H-spiperone binding sites in striatal membranes, indicating supersensitivity of the postsynaptic receptors. Subsequent prolonged treatment with high doses of L-DOPA/carbidopa resulted in a decrease in 3H-spiperone binding sites, but had no effect on the supersensitive presynaptic receptors. It is suggested that tardive dyskinesia may be a state of both pre- and postsynaptic dopamine receptor supersensitivity and that chronic L-DOPA treatment may have a differential effect on these sites.     

Low-cost printing of poly(dimethylsiloxane) barriers to define microchannels in paper

This paper describes the use of a modified x,y-plotter to generate hydrophilic channels by printing a solution of hydrophobic polymer (pol(dimethylsiloxane; PDMS) dissolved in hexanes onto filter paper. The PDMS penetrates the depth of the paper and forms a hydrophobic wall that aqueous solutions cannot cross. The minimum size of printed features is approximately 1 mm; this resolution is adequate for the rapid prototyping of hand-held, visually read, diagnostic assays (and other microfluidic systems) based on paper. After curing the printed PDMS, the paper-based devices can be bent or folded to generate three-dimensional systems of channels. Capillary action pulls aqueous samples into the paper channels. Colorimetric assays for the presence of glucose and protein are demonstrated in the printed devices; spots of Bromothymol Blue distinguished samples with slightly basic pH (8.0) from samples with slightly acidic pH (6.5). The work also describes using printed devices that can be loaded using multipipets and printed flexible, foldable channels in paper over areas larger than 100 cm2.     

Self-assembly of peptide nanotubes and amyloid-like structures by charged-termini-capped diphenylalanine peptide analogues

We had recently demonstrated that the diphenylalanine peptide, the core recognition motif of the Alzheimer's ß-amyloid polypeptide, self-assembles into a novel class of peptide nanotubes. The formation of well-ordered supramolecular structures at the nanoscale by such a simple peptide was consistent with our suggestion that aromatic interactions may provide order and directionality needed for the formation of fibrillar peptide structures. Yet, we could not rule out a contribution of the charged amine and carboxyl moieties at the termini of the short peptide. In order to explore the potential role of electrostatic interaction in the assembly process we have studied a modified non-charged peptide analogue, Ac-Phe–Phe-NH₂, in which the N-terminal amine was acetylated and the C-terminal carboxyl was amidated. Scanning and transmission electron microscopy analyses demonstrated that this peptide analogue self-assembles into highly-ordered tubular structures, as observed with the NH₂-Phe–Phe-COOH. Also, infrared spectroscopy revealed an amide I absorbance pattern that is very similar to that of the non-modified peptide. Furthermore, an amidated NH₂-Phe–Phe-NH₂ peptide, which has a net positive charge, also self-assembled into ordered tubular structures. On the other hand, the amine-modified analogues Boc-Phe–Phe-COOH, Z-Phe–Phe-COOH, and Fmoc-Phe–Phe-COOH peptides formed amyloid-like structures that had a significantly smaller diameter. Taken together, the current study further supports our hypothesis regarding the role of aromatic interactions in the self-assembly of amyloid fibrils and amyloid-associated nanostructures that can be modulated by simple chemical modifications.     

rexB of bacteriophage lambda is an anti-cell death gene

In Escherichia coli, programmed cell death is mediated through "addiction modules" consisting of two genes; the product of one gene is long-lived and toxic, whereas the product of the other is short-lived and antagonizes the toxic effect. Here we show that the product of lambdarexB, one of the few genes expressed in the lysogenic state of bacteriophage lambda, prevents cell death directed by each of two addiction modules, phd-doc of plasmid prophage P1 and the rel mazEF of E. coli, which is induced by the signal molecule guanosine 3',5'-bispyrophosphate (ppGpp) and thus by amino acid starvation. lambdaRexB inhibits the degradation of the antitoxic labile components Phd and MazE of these systems, which are substrates of ClpP proteases. We present a model for this anti-cell death effect of lambdaRexB through its action on the ClpP proteolytic subunit. We also propose that the lambdarex operon has an additional function to the well known phenomenon of exclusion of other phages; it can prevent the death of lysogenized cells under conditions of nutrient starvation. Thus, the rex operon may be considered as the "survival operon" of phage lambda.     

Novel electrochemical biosensing platform using self-assembled peptide nanotubes

Here we describe a novel electrochemical biosensing platform based on biocompatible, well-ordered, self-assembled diphenylalanine peptide nanotubes. Voltammetric and time-based amperometric techniques were applied to demonstrate the ability of the peptide nanotubes to improve the electrochemical parameters of graphite electrodes. The findings clearly show that this novel class of peptide nanotubes provides an attractive component for future electroanalytical devices.     

An improved algorithm for online coloring of intervals with bandwidth

We present an improved online algorithm for coloring interval graphs with bandwidth. This problem has recently been studied by Adamy and Erlebach and a 195-competitive online strategy has been presented. We improve this by presenting a 10-competitive strategy. To achieve this result, we use variants of an optimal online coloring algorithm due to Kierstead and Trotter.