Intracellular expression of a functional short peptide confers resistance to apoptosis

Expression of free short peptides could potentially be used to modulate biochemical cascades and consequently to change cellular phenotypes. Here we demonstrate that expression of a short peptide of 15 amino acids, including the pseudo-substrate site of the baculovirus-apoptosis inhibitor P35, Asp-Gln-Met-Asp (DQMD), leads to abrogation of the apoptotic cascade. Treatment of cells, expressing the DQMD peptide with two apoptosis inducers, etoposide and sodium nitroprusside, (SNP) results in blocking of the apoptotic cascade, indicated by DNA fragmentation and caspase activation. Consequently, stable expression of the DQMD peptide led to protection of cells, following induction of apoptosis and to the outgrowth and enrichment of resistant cell colonies. The results presented in this work demonstrate for the first time the feasibility of expressing in cells functional short peptides that block apoptotic cascade, and to rescue the phenotypically altered cells in a stable fashion. This approach is general and could be applied to the study of other peptides and the respective biochemical cascades.     

Stochastic emergence of repeating cortical motifs in spontaneous membrane potential fluctuations in vivo

It was recently discovered that subthreshold membrane potential fluctuations of cortical neurons can precisely repeat during spontaneous activity, seconds to minutes apart, both in brain slices and in anesthetized animals. These repeats, also called cortical motifs, were suggested to reflect a replay of sequential neuronal firing patterns. We searched for motifs in spontaneous activity, recorded from the rat barrel cortex and from the cat striate cortex of anesthetized animals, and found numerous repeating patterns of high similarity and repetition rates. To test their significance, various statistics were compared between physiological data and three different types of stochastic surrogate data that preserve dynamical characteristics of the recorded data. We found no evidence for the existence of deterministically generated cortical motifs. Rather, the stochastic properties of cortical motifs suggest that they appear by chance, as a result of the constraints imposed by the coarse dynamics of subthreshold ongoing activity.     

Identification of palindromic sequences recognized by restriction endonucleases, as based on the tabularized sequencing data for seven viral and plasmid DNAs

Computer search of DNA sequences for phages φX174, G4, M13 and fd, plasmids pBR322 and pA03, and virus SV40, was employed to prepare tables specifying the size classes and frequencies of DNA segments located between all possible tetra-, penta- and hexanucleotide palindromes. As described earlier (Fuchs et al., 1978), these tables permit identifying sequences recognized by most of the restriction endonucleases. The effect of sequencing errors on the accuracy of the present identification method is evaluated. Only four of the 224 listed sequences do not appear in any of the seven DNAs, leading to discussion (see Appendix) on the natural sequence distribution.     

Characterization of a dockerin-based affinity tag: application for purification of a broad variety of target proteins

Cellulose, a major component of plant matter, is degraded by a cell surface multiprotein complex called the cellulosome produced by several anaerobic bacteria. This complex coordinates the assembly of different glycoside hydrolases, via a high-affinity Ca(2+)-dependent interaction between the enzyme-borne dockerin and the scaffoldin-borne cohesin modules. In this study, we characterized a new protein affinity tag, ΔDoc, a truncated version (48 residues) of the Clostridium thermocellum Cel48S dockerin. The truncated dockerin tag has a binding affinity (K(A)) of 7.7 × 10(8)M(-1), calculated by a competitive enzyme-linked assay system. In order to examine whether the tag can be used for general application in affinity chromatography, it was fused to a range of target proteins, including Aequorea victoria green fluorescent protein (GFP), C. thermocellum β-glucosidase, Escherichia coli thioesterase/protease I (TEP1), and the antibody-binding ZZ-domain from Staphylococcus aureus protein A. The results of this study significantly extend initial studies performed using the Geobacillus stearothermophilus xylanase T-6 as a model system. In addition, the enzymatic activity of a C. thermocellum β-glucosidase, purified using this approach, was tested and found to be similar to that of a β-glucosidase preparation (without the ΔDoc tag) purified using the standard His-tag. The truncated dockerin derivative functioned as an effective affinity tag through specific interaction with a cognate cohesin, and highly purified target proteins were obtained in a single step directly from crude cell extracts. The relatively inexpensive beaded cellulose-based affinity column was reusable and maintained high capacity after each cycle. This study demonstrates that deletion into the first Ca(2+)-binding loop of the dockerin module results in an efficient and robust affinity tag that can be generally applied for protein purification.     

Self-assembled monolayers of polythiophene conductive polymers improve biocompatibility and electrical impedance of neural electrodes

There is continued interest in the development of conductive polymer coatings to improve the electrical properties and biocompatibility of electrodes for neural prostheses. We present here a new type of coating, based on mixed self-assembled monolayers (SAMs) of thiolated poly(alkylthiophene)s and functionalized alkanethiols. When assembled as a SAM on electrodes designed for in vitro electrophysiology, these polymers are able to significantly lower electrode impedance at 1 kHz. The same mixed formulation is able to promote the outgrowth of neurites from primary mouse cortical neurons when the alkanethiol component is functionalized with a neural cell adhesion molecule (NCAM) binding antibody. Atomic force microscopy of the SAMs shows that they exert their effect through the well-known mechanism of increasing electrode surface area. These new covalently bound films have the potential to be more robust and are more controllable in their composition than existing electrodeposited conductive polymer coatings.     

Human cytomegalovirus UL97 kinase and nonkinase functions mediate viral cytoplasmic secondary envelopment

Previous studies have revealed critical roles for the human cytomegalovirus (HCMV) UL97 kinase in viral nuclear maturation events. We have shown recently that UL97 affects the morphology of the viral cytoplasmic assembly compartment (AC) (M. Azzeh, A. Honigman, A. Taraboulos, A. Rouvinski, and D. G. Wolf, Virology 354:69-79, 2006). Here, we employed a comprehensive ultrastructural analysis to dissect the impact of UL97 on cytoplasmic steps of HCMV assembly. Using UL97 deletion (ΔUL97) and kinase-null (K355M) mutants, as well as the UL97 kinase inhibitor NGIC-I, we demonstrated that the loss of UL97 kinase activity resulted in a unique combination of cytoplasmic features: (i) the formation of pp65-rich aberrant cytoplasmic tegument aggregates, (ii) distorted intracytoplasmic membranes, which replaced the normal architecture of the AC, and (iv) a paucity of cytoplasmic tegumented capsids and dense bodies (DBs). We further showed that these abnormal assembly intermediates did not result from impaired nuclear capsid maturation and egress per se by using 2-bromo-5,6-dichloro-1-(β-d-ribofuranosyl) benzimidizole (BDCRB) to induce the artificial inhibition of nuclear maturation and the nucleocytoplasmic translocation of capsids. The specific abrogation of UL97 kinase activity under low-multiplicity-of-infection conditions resulted in the improved release of extracellular virus compared to that of ΔUL97, despite similar rates of viral DNA accumulation and similar effects on nuclear capsid maturation and egress. The only ultrastructural correlate of the growth difference was a higher number of cytoplasmic DBs, tegumented capsids, and clustered viral particles observed upon the specific abrogation of UL97 kinase activity compared to that of ΔUL97. These combined findings reveal a novel role for UL97 in HCMV cytoplasmic secondary envelopment steps, with a further distinction of kinase-mediated function in the formation of the virus-induced AC and a nonkinase function enhancing the efficacy of viral tegumentation and release.