siRNA, miRNA and HIV: promises and challenges

INTRODUCTION The recent discovery of small interfering RNA (siRNA) revealed an important role for small RNAs in regulating gene expression. First described in plants, as “post- trancriptional gene silencing” (PTGS) [1], RNA interfer- ence (RNAi) is a nucleic-acid based immune defense against viruses, transgenes and transposons [2]. Triggered by double-stranded RNA (dsRNA), RNAi leads to the se- quence specific degradation of a target mRNA [3]. In eukaryotic cells, long dsRN…     

Ketamine pretreatment exacerbated 3,4-methylenedioxymethamphetamine-induced central dopamine toxicity

Currently, joint use of ketamine and 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) represents a specific combination of polydrug abuse. Long-lasting and even aggravated central neuronal toxicity associated with mixing ketamine and MDMA use is of special concern. This study was undertaken to examine the modulating effects of ketamine treatment on later MDMA-induced dopamine and serotonin neurotoxicity. We found that repeated administration of ketamine (50 mg/kg x 7) at 1.5-h intervals did not render observable dopamine or serotonin depletion in catecholaminergic target regions examined. In contrast, three consecutive doses of MDMA (20 mg/kg each) at 2-h intervals produced long-lasting dopamine and serotonin depletions in striatum, nucleus accumbens and prefrontal cortex. More importantly, pretreatment with binge doses of ketamine (50 mg/kg x 7 at 1.5-h intervals) 12 h prior to the MDMA dosing regimen (20 mg/kg x 3 at 2-h intervals) aggravated the MDMA-induced dopaminergic toxicity. Nonetheless, such binge doses of ketamine treatment did not affect MDMA-induced serotonergic toxicity. These results, taken together, indicate that binge use of ketamine specifically enhances the MDMA-induced central dopaminergic neurotoxicity in adult mouse brain.     

Determination of binding potency of peptidic inhibitors of Grb2-SH2 by using the protein-captured biosensor method

The growth factor receptor-binding protein 2-Src homology 2 (Grb2-SH2) domain plays an important role in the oncogenic Ras signal transduction pathway, therefore, peptidic inhibitors of the Grb2-SH2 domain has been chosen as our target for the development of antiproliferative agents. The inhibitory effects of peptide analogs on the Grb2-SH2 domain have been determined by using surface plasmon resonance (SPR) technology developed with the BIACORE biosensor. Recently, we reported the analysis of interactions between peptides and the GST-Grb2-SH2 that was immobilized on the surface of sensor chip by using BIACORE biosensor (the protein-immobilized method). Herein, we analyze interactions of peptides with the GST-Grb2-SH2 that was captured by the anti-GST antibodies immobilized on the surface of sensor chip (the protein-captured method). Results obtained by both methods are in good correlation, indicating the immobilization of GST-Grb2-SH2 on the sensor chip did not significantly affect the binding of Grb2-SH2 with peptides. Both SPR-based assays are very sensitive bioanalytical methods and can be applied in screening inhibitors of target proteins or purifying GST-fusion proteins, however, considering the efficiency and the cost, the GST-Grb2-SH2-immobilized method is suggested for routinely determining the binding potency of inhibitors of Grb2-SH2.     

Phytase activity in tobacco (Nicotiana tabacum) root exudates is exhibited by a purple acid phosphatase

Phytases are enzymes that catalyze liberation of inorganic phosphates from phytate, the major organic phosphorus in soil. Tobacco (Nicotiana tabacum) responds to phosphorus starvation with an increase in extracellular phytase activity. By a three-step purification scheme, a phosphatase with phytase activity was purified 486-fold from tobacco root exudates to a specific activity of 6,028 nkat mg(-1) and an overall yield of 3%. SDS-PAGE revealed a single polypeptide of 64 kDa, thus indicating apparent homogeneity of the final enzyme preparation. Gel filtration chromatography suggested that the enzyme was a ca. 56 kDa monomeric protein. De novo sequencing by tandem mass spectrometry resulted in a tryptic peptide sequence that shares high homology with several plant purple acid phosphatases. The identity of the enzyme was further confirmed by molybdate-inhibition assay and cDNA cloning. The purified enzyme exhibited pH and temperature optima at 5.0-5.5 and 45 degrees C, respectively, and were found to have high affinities for both p-nitrophenyl phosphate (pNPP; K(m)=13.9 microM) and phytate (K(m)=14.7 microM), but a higher kcat for pNPP (2,056 s(-1)) than phytate (908 s(-1)). Although a broad specificity of the enzyme was observed for a range of physiological substrates in soil, maximum activity was achieved using mononucleotides as substrates. We conclude that the phytase activity in tobacco root exudates is exhibited by a purple acid phosphatase and its catalytic properties are pertinent to its role in mobilizing organic P in soil.     

Genbank accession #: AF 124983

Plant Molecular Biology -     

Characterization of Neutralizing Antibodies and Identification of Neutralizing Epitope Mimics on the Clostridium botulinum Neurotoxin Type A

Clostridium botulinum neurotoxin type A (BTx-A) is known to inhibit the release of acetylcholine at the neuromuscular junctions and synapses and to cause neuroparalysis and death. In this study, we have identified two monoclonal antibodies, BT57-1 and BT150-3, which protect ICR mice against lethal doses of BTx-A challenge. The neutralizing activities for BT57-1 and BT150-3 were 10³ and 10⁴ times the 50% lethal dose, respectively. Using immunoblotting analysis, BT57-1 was recognized as a light chain and BT150-3 was recognized as a heavy chain of BTx-A. Also, applying the phage display method, we investigated the antibodies' neutralizing B-cell epitopes. These immunopositive phage clones displayed consensus motifs, Asp-Pro-Leu for BT57-1 and Cys-X-Asp-Cys for BT150. The synthetic peptide P4M (KGTFDPLQEPRT) corresponded to the phage-displayed peptide selected by BT57-1 and was able to bind the antibodies specifically. This peptide was also shown by competitive inhibition assay to be able to inhibit phage clone binding to BT57-1. Aspartic acid (D⁵) in P4M was crucial to the binding of P4M to BT57-1, since its binding activity dramatically decreased when it was changed to lysine (K⁵). Finally, immunizing mice with the selected phage clones elicited a specific humoral response against BTx-A. These results suggest that phage-displayed random-peptide libraries are useful in identifying the neutralizing epitopes of monoclonal antibodies. In the future, the identification of the neutralizing epitopes of BTx-A may provide important information for the identification of the BTx-A receptor and the design of a BTx-A vaccine.